Image forming apparatus, drum unit, image forming module, and method of insertion and removal of a damper into and from an image carrier drum

ABSTRACT

An image forming apparatus includes a photoreceptor belt formed by either a belt or a thin-walled cylinder. A charging unit that sets bias characteristics of the photoreceptor belt has an arrangement to approach towards the photoreceptor belt. A damper is provided on a side of the photoreceptor belt opposite to the side facing the charging unit. The damper absorbs vibrations in the photoreceptor belt through a supporting plate.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a technology for preventing noisecaused by vibrational resonance produced in a latent image carrier dueto a thin-walled structure of an image forming apparatus.

2) Description of the Related Art

In image forming apparatuses like a copying machine, a facsimile, aprinter, and a printing machine, steps of charging, writing, developing,and transferring are carried out for a photoreceptor as a latent imagecarrier. In the step of transferring, a toner image that is transferredon a recording medium like a recording paper is fixed to give a copy ora printout.

A structure that employs a non-contact charging method with aerialdischarge using a corona charger is used for charging of thephotoreceptor. However, in the structure, discharge products like ozoneand nitrogen oxide are generated during discharging which may result indeterioration of environment or deterioration of chargingcharacteristics on the photoreceptor. Therefore, a contact chargingmethod, which does not generate the problems and enables to apply lowvoltage, is proposed as a substitute for an aerial discharge. Astructure that injects charge by applying voltage between thephotoreceptor and any one of a brush, a roller, and a blade of aconductive material that is kept in contact with the photoreceptor isknown as one of the contact charging methods.

In the contact charging method, it is possible to apply low voltage andthere is no generation of discharge products. However, since any one ofa brush, a roller, and a blade made of a conductive material is indirect contact with the photoreceptor, it is easy to carry out reversetransition of deposits of toner etc. that remain on the photoreceptor.The deposits that have undergone reverse transition hinder the injectionof charge and may deteriorate the charging characteristics. Furthermore,when a charging member is left without being used in a charging processfor hours, a portion of the charging member that is in contact with thephotoreceptor, changes shape due to permanent deformation. As a result,when the charging process is carried out again, there is no uniformcontact of the charging member with the surface of the photoreceptor,which may result in charging unevenness.

To solve this problem, a unit that forms a charging range between thephotoreceptor and the charging member is proposed. The charging memberis disposed so that a prescribed minute interval is maintained betweenthe photoreceptor and the charging member. The unit is an intermediatestructure of non-contact and contact charging methods. A charging method(proximity charging method) has been employed in recent years. In thismethod, a prescribed minute interval is provided between thephotoreceptor and the charging member such as a brush, a roller, and ablade of a conductive material, and charging is carried out by applyingeither of only dc voltage and dc voltage superimposed by an ac voltage.

In a structure which employs the proximity charging method, in a casewhere the charging member is a roller, a film of prescribed thickness iswound on both ends of the charging roller in its axial direction forsetting of a gap and size of the minute gap is prescribed by thicknessof the film.

Maintaining the prescribed size of the minute gap is an importantcondition to have no variation in the charging characteristics. When itis assumed that the size of the minute gap is maintained, the uniformcharging becomes possible by applying of dc voltage for which setting iscomparatively easy. However, when the size of the gap variesconsiderably, there is a considerable variation in a charging electricalpotential in proportion to the variation in the size of the gap.Therefore, conventionally, various ideas have been thought up to achieveuniform charging characteristics even in a case where the size of thegap is varied by superimposing ac voltage on dc voltage.

On the other hand, apart from the charging unit, a developing unit isthere to set the charging characteristics, i.e. bias characteristics. Ina case of the developing unit, a developing method that uses either of aone-component developer and a two-component developer, is known. In thedeveloping unit which uses the two-component developer, a developer thatincludes a carrier made of a magnetic material (substance) for aninsulating toner, is agitated by an agitator. The toner is thendeposited by charging on the carrier and the developer is made to be incontact with the photoreceptor.

In a developer carrier used in the developing unit, a developing sleeve,which can carry the developer on its surface, is used and a magneticroll with a plurality of south poles and north poles lined upalternately on it is provided inside the developing sleeve. In thedeveloper carrier, the developer is drawn up by magnetic force of themagnetic roll and a magnetic brush is formed by making the developererected in the form of a brush on the surface of the developer carrier.

When the magnetic brush carried on the surface of the magnetic sleevecomes in contact with the electrostatic latent image that is formed onthe photoreceptor based on either of image information and a paperdocument image, a developing bias is applied between the photoreceptorand the magnetic sleeve as the developer carrier. Due to the developingbias, the toner in the magnetic brush undergoes electrostatic absorptionby the electrostatic latent image thereby forming a toner image.

As a developing bias, a bias as follows is used. The bias superimposesthe ac voltage on the dc voltage to improve the developing capability,carry out the developing to the electrostatic latent image identicallywith utmost clarity, and improve uniformity of dots. Moreover, the biashas a first peak value V1 for transferring the toner from the developercarrier to the photoreceptor and a second peak value V2 for transferringthe toner from the photoreceptor to the developer carrier. A methodusing the bias as a developer bias, in which a vibrating electric fieldis created in a developing area between the developer carrier and thephotoreceptor and charged toner is applied on the photoreceptor, isknown.

For the ac voltage which is superimposed on dc voltage, a rectangularwaveform as in FIG. 44, a sine waveform as in FIG. 45, a triangularwaveform as in FIG. 46, or a duty bias as shown in FIG. 47 is used.

In a case of using the duty bias shown in FIG. 47, a ½ value of thewaveform differs from an average value of time integral. In FIG. 47,such a bias as follows is used. That is, the bias includes a timerequired for application of the first peak value V1 and a time requiredfor application of the second peak value V2. At the first peak value V1,an electric field is created such that the electric field is biased in adirection in which the toner is transferred from the developing sleeveto the photoreceptor. At the second peak value V2, an electric field iscreated such that the electric field is biased in a direction in whichthe toner is transferred from the photoreceptor to the developingsleeve.

In a case of using the duty bias, by optimizing a frequency of acvoltage, a duty ratio (=t1/(t1+t2)×100% in FIG. 47), and a peak-to-peakvalue i.e. a difference between a maximum value of ac voltage (V1) and aminimum value of ac voltage (V2), it is possible to deposit the tonerefficiently on an image area of the photoreceptor or not to deposit thetoner on non-image area of the photoreceptor. Moreover, the optimizationalso enables the adjustment for increasing the density of an image whileimproving the uniformity of toner dots identical to the latent image.

Among methods which use the other developer i.e. the one-componentdeveloper, a jumping developing is a known method. In the jumpingdeveloping, an electrostatic latent image on the photoreceptor isdeveloped while the developing sleeve as the developer carrier of thedeveloping unit and the photoreceptor are maintained in the non-contactstate. In the jumping developing, a layer of the one-component developeris formed on the developing sleeve. More specifically, a magnetic rollhaving a plurality of south poles and north poles lined up alternatelyon it and facing the electrostatic latent image carrier, is fixed on thedeveloping sleeve. Furthermore, a toner brush is formed in a developingarea and the developer (toner) is splashed and applied on thephotoreceptor by applying a developing bias obtained by superimposing anac component on a dc component, to the developing sleeve. Fogged toneris then returned in the direction of the developing sleeve and thelatent image is visualized as a toner image.

When the developer is a one-component developer, in the same manner asthe two-component developer, the developing bias method is used. In thedeveloping bias method, by varying the peak-to-peak value, frequency,and duty ratio, it is possible to deposit the toner efficiently on theimage area of the photoreceptor or not to deposit the toner on thenon-image area of the photoreceptor. Moreover, the image density isincreased while improving the uniformity of toner dots.

Depending on a setting of the bias characteristics that is carried outin the charging unit and the developing unit, noise is caused byapplying ac voltage during shifting of the photoreceptor. Following is areason for the generation of noise. A lighter weight conductive materialin cylindrical form is used for the photoreceptor. Concretely, analuminum cylinder having thin walls is used for the photoreceptor with astructure that resonates easily. Besides, not only units used incharging and developing processes are disposed facing the photoreceptor,but units for carrying out writing, transferring, and cleaning processesare also disposed facing the photoreceptor. In particular, the unit thatcarries out the cleaning process is disposed close to the photoreceptor,other than the units for charging process and developing process.Therefore, the photoreceptor can resonate easily due to vibratingelectric field created when ac voltage is applied. Furthermore, due to acleaning blade of the cleaning unit that is in contact with thephotoreceptor, the vibrations are generated in the thin-walled cylinderdue to repetition of deformation and restoration of shape of thecleaning blade when the cleaning blade scrapes the photoreceptor, andresonance in the photoreceptor produces noise.

That is, the image forming apparatuses like a copying machine, aprinter, a facsimile, or a multifunction machine including any functionsof these have been known widely. The image carrier drum includes eitherof a photoreceptor drum on surface of which a toner image is formed bycharging, exposing, and developing and an intermediate transfer drum onsurface of which a toner image is transferred from the photoreceptor andformed. The image carrier drum vibrates due to an external force thatimparts vibrations, thereby resulting in generation of noise from theimage carrier drum. For example, image forming units like a chargingunit and a cleaning unit are provided around the photoreceptor drum. Thecharging member vibrates due to effect of ac voltage applied to thecharging unit. The charging member vibrates due to stick-slip which iscaused by the cleaning blade that is in pressed contact with the surfaceof the image carrier drum. The stick-slip starts as the image carrierdrum rotates. The vibrations are transmitted to the image carrier drumto make the image carrier drum vibrate, and to thereby generate noise. Auser may feel unpleasant because of noise. Therefore, measures have beentaken in conventional techniques by providing the damper inside theimage carrier drum to minimize vibrations of the image carrier drum toreduce the noise.

On the other hand, an image forming apparatus explained below has beenin practical use to enable conservation of energy. The image formingapparatus uses a toner having a low melting point, and is structuredsuch that a transferred toner image can be fixed on the recording mediumat comparatively low temperature. However, a case of using the tonerhaving a low melting point tend to generate noise easily as compared toa case of using a toner having a high melting point. Therefore, it isfound that the conventional damper is unable to reduce the noisesufficiently. It is not sure that the use of the toner having a lowmelting point increases the noise. However, additives like wax or thelike contained in the toner tend to stick to the surface of the imagecarrier drum. Since the amount of the additive that is deposited becomesnon-uniform depending on an image pattern, a component like the cleaningblade in contact with the surface of the image carrier drum does notmove uniformly. It is considered that loud noise that is generated inthe image carrier drum is due to vibrations caused by non-uniformmovement of the cleaning blade.

A structure in which the photoreceptor is made solid i.e. a solidcylinder has been disclosed, for example, in Japanese Patent ApplicationLaid Open Publication (“JPA”) No. HEI 07-72641, as the conventionalstructures to reduce the noise. Furthermore, a structure in which atleast two of an elastic body and a cylinder member are fitted inside thephotoreceptor and resonance in peripheral wall of the thin-walledcylinder is reduced has been disclosed in JPA No. HEI 11-184308, for thesame purpose.

Moreover, there is another structure made by using a cylinder unit inwhich the damper is inserted inside the cylinder to reduce vibrations ofthe cylinder and therefore the noise is minimized. This type ofstructure has been disclosed in JPA No. HEI 11-35167 and JPA No. HEI10-97158.

In recent years, products which can be recycled are promoted with anobject of protection of environment and saving of resources. Same thingis expected about the cylinder unit. To have better recycling of aproduct formed by a plurality of components, it is necessary that theproduct be structured in such a way that each component of the productcan be dismantled easily after the product is used and the dismantledcomponent can be reused or can be reprocessed. However, in theconventional cylinder unit, the damper inserted inside the cylinder isfixed to the cylinder and therefore it is difficult to remove the damperfrom the cylinder. Thus, the conventional cylinder unit is founddifficult to be recycled.

However, in the structure for prevention of noise, increase in cost ofthe photoreceptor and complications in structures are matters ofconcern. When the photoreceptor is structured using a solid body, it notonly raises the cost but also increases weight. Due to increase in theweight, there is an increase in driving force required for rotation,which results in increase in inertial force. The increase in weight ofthe photoreceptor affects its portability, which may result in damagingthe surface of the photoreceptor or causing an injury to a person due toheavy weight on dropping of the photoreceptor during replacement job. Ifa plurality of damping structures are provided inside the photoreceptor,there is a rise in cost due to the increased number of components andassembling processes.

Moreover, the image forming apparatus that uses the toner having a lowmelting point tends to generate noise easily as compared to the case ofusing the toner having a high melting point. Therefore, the conventionaldamper is unable to reduce the noise sufficiently.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve at least the problemsin the conventional technology.

According to one aspect of this invention, an image forming apparatusincludes a latent image carrier that includes an arrangement of any of abelt and a thin walled hollow cylinder, the latent image carrier havinga first surface and a second surface. The apparatus also includes a biasapplying unit that has an arrangement for approaching towards the firstsurface of the latent image carrier, in which the bias applying unitsets bias characteristics of the latent image carrier. The apparatusfurther includes a vibration absorber that absorbs vibrations in thelatent image carrier, in which the vibration absorber is made to touchthe second surface of the latent image carrier.

According to another aspect of this invention, an image formingapparatus includes a toner image forming unit that forms a toner imageon an image carrier drum using a toner having an outflow starttemperature less than or equal to 102° C. measured by flow testermethod. The apparatus also includes a damper provided inside the imagecarrier drum, in which the damper is made of a material with a tangentof loss tan δ of the damper is greater than or equal to 0.5. The tangentof loss is a value of damping effect.

According to still another aspect of this invention, a drum unitincludes a cylinder, a shaft that extends inside and supports thecylinder, and a damper disposed inside the cylinder. The cylinder, theshaft, and the damper are assembled such that when the shaft is pulledout from the cylinder, the damper moves in the axial direction of thecylinder together with the shaft and is removed from the cylinder.

According to still another aspect of this invention, an image formingmodule includes an image carrier drum, and a shaft that extends insideand supports the drum. The module also includes a damper disposed insidethe drum, in which the drum, the shaft, and the damper are assembledsuch that when the shaft is pulled out from the drum, the damper movesin the axial direction of the drum together with the shaft and isremoved from the drum. The module further includes an image formingelement that forms an image on the drum. The image carrier drum and theimage forming element are assembled together as an integrated assembly.

According to still another aspect of this invention, the image formingapparatus includes an image carrier drum, a shaft that extends insideand supports the drum, and a damper disposed inside the drum. The drum,the shaft, and the damper are assembled such that when the shaft ispulled out from the drum, the damper moves in the axial direction of thedrum together with the shaft and is removed from the drum.

According to still another aspect of this invention, a method ofinsertion and removal of a damper into and from an image carrier drumincludes inserting the damper into the image carrier drum from anopening on one end in an axial direction of the image carrier drum andthereby mounting the damper inside the drum. The method also includesremoving the damper from an opening on other end in the axial directionof the image carrier drum.

According to still another aspect of this invention, a drum unitincludes an image carrier drum, and a damper. The damper is insertedinto the image carrier drum from an opening on one end in an axialdirection of the image carrier drum to thereby mount the damper insidethe drum, and the damper mounted inside the drum is removed from anopening on other end in the axial direction of the image carrier drum.

According to still another aspect of this invention, an image formingmodule includes a drum unit having an image carrier drum and a damper,in which the damper is inserted into the image carrier drum from anopening on one end in an axial direction of the image carrier drum tothereby mount the damper inside the drum, and the damper mounted insidethe drum is removed from an opening on other end in the axial directionof the image carrier drum. The module also includes an image formingunit that forms a toner image on the image carrier drum. The drum unitand the image forming unit are detachable from a main body of the imageforming apparatus.

According to still another aspect of this invention, an image formingapparatus includes an image forming module. The image forming moduleincludes a drum unit having an image carrier drum, and a damper, inwhich the damper is inserted into the image carrier drum from an openingon one end in an axial direction of the image carrier drum to therebymount the damper inside the drum, and the damper mounted inside the drumis removed from an opening on other end in the axial direction of theimage carrier drum. The apparatus also includes an image forming unitthat forms a toner image on the image carrier drum. The drum unit andthe image forming unit are detachable from a main body of the imageforming apparatus.

According to still another aspect of this invention, an image formingapparatus includes a drum unit having an image carrier drum to form atoner image and a damper. The damper is inserted into the image carrierdrum from an opening on one end in an axial direction of the imagecarrier drum to thereby mount the damper inside the drum, and the dampermounted inside the drum is removed from an opening on other end in theaxial direction of the image carrier drum.

The other objects, features and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed descriptions of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an image forming unit in an imageforming apparatus according to a first embodiment of the presentinvention;

FIG. 2 illustrates a roller around which a photoreceptor belt used inthe image forming unit shown in FIG. 1 is wound;

FIG. 3 illustrates another structure of the roller shown in FIG. 2;

FIG. 4 illustrates still another structure of the roller shown in FIG.2;

FIG. 5 illustrates still another structure of the roller shown in FIG.2;

FIG. 6 illustrates a structure for prevention of noise in the imageforming apparatus shown in FIG. 1;

FIG. 7 illustrates another example of the structure for prevention ofnoise shown in FIG. 6;

FIG. 8 illustrates a photoreceptor belt used in the image formingapparatus shown in FIG. 1;

FIG. 9 illustrates another example of the image forming apparatus;

FIG. 10 illustrates a developing unit used in the image formingapparatus shown in FIG. 9;

FIG. 11 illustrates a latent image carrier used in the image formingapparatus in FIG. 9;

FIG. 12 illustrates another structure of the latent image carrier usedin the image forming apparatus in FIG. 11;

FIG. 13 is a graphical of noise characteristics in the structure of thelatent image carriers shown in FIG. 11 and FIG. 12;

FIG. 14 illustrates an application related to the image formingapparatus;

FIG. 15 is a schematic diagram of an image forming unit in an imageforming apparatus according to a second embodiment of the presentinvention;

FIG. 16 is a longitudinal cross section of an image carrier drum with adamper disposed inside the drum;

FIG. 17 is a longitudinal cross section of a damper which is differentin shape than the damper in FIG. 16;

FIG. 15 illustrates a charging roller that is in contact with a surfaceof the image carrier drum;

FIG. 19 illustrates a charging unit formed by a brush roller;

FIG. 20 illustrates a charging unit formed by a magnetic brush unit;

FIG. 21 is a schematic diagram of an image forming unit in an imageforming apparatus according to a third embodiment of the presentinvention;

FIG. 22 is a longitudinal cross section of a cylinder unit in FIG. 21;

FIG. 23 is an exploded perspective view of an image carrier drum and aflange in FIG. 22;

FIG. 24 is a cross section of a state when a shaft and a damper aremoved from the state shown in FIG. 22;

FIG. 25 is a cross section of another example of the damper;

FIG. 26 is a cross section of still another example of the damper;

FIG. 27 is a cross section of still another example of the damper;

FIG. 28 is a cross section of still another example of the damper;

FIG. 29 is a cross section of a cylinder unit in which a flange having afirst cylinder member and a second cylinder member is used;

FIG. 30 is a perspective view of the first and the second cylindermembers;

FIG. 31 is a cross section of a state while the first and the secondcylinder members are assembled with the image carrier drum;

FIG. 32 is a schematic diagram of an image forming unit in an imageforming apparatus according to a fourth embodiment of the presentinvention;

FIG. 33 is a longitudinal cross section of a drum unit in FIG. 32;

FIG. 34 is a cross section of a state before the damper is inserted intothe image carrier drum;

FIG. 35 is a cross section of a state after the damper is inserted intothe image carrier drum;

FIG. 36 is a cross section of a state when the damper has come incontact with the flange;

FIG. 37 is a cross section of a state when the damper is pushed outfurther after the flange is removed from the image carrier drum;

FIG. 38 is a cross section of an example of inserting and removing thedamper into and from the image carrier drum by pulling the damper by aforce imparting member;

FIG. 39 is a longitudinal cross section of another example of the drumunit;

FIG. 40 is a cross section of a state after the shaft and the damper aremoved from positions shown in FIG. 39;

FIG. 41 is a cross section of a drum unit in which the damper is formedby a compression coil spring;

FIG. 42 is a cross section of an example of using the flange having afirst and a second flange members;

FIG. 43 is schematic cross section of another example of the imageforming apparatus;

FIG. 44 is a graph of an example of a developing bias;

FIG. 45 is a graph of another example of the developing bias;

FIG. 46 is a graph of still another example of the developing bias; and

FIG. 47 is a graph of still another example of the developing bias.

DETAILED DESCRIPTION

Exemplary embodiments of an image forming apparatus, a drum unit, animage forming module, and a method for insertion and removal of a damperinto and from an image carrier drum are explained in detail below withreference to the accompanying drawings. The present invention is notlimited only to the following embodiments.

FIG. 1 is a schematic diagram of an image forming unit of an imageforming apparatus 100 according to a first embodiment. In the imageforming apparatus 100, a photoreceptor that functions as a latent imagecarrier, is formed by a belt (hereinafter, “photoreceptor belt 101”).The photoreceptor belt 101 is wound around among a plurality of rollers102 to 104 and can move in a direction indicated by an arrow A. Acharging unit 105, a writing unit 106 (in FIG. 1, only optical path isshown), a developing unit 107, a transferring unit 108, and a cleaningunit 109 are disposed around the photoreceptor belt 101 along thedirection of movement of the belt to carry out image forming processing.

The rollers 102 to 104 are arranged such that the photoreceptor belt 101forms a triangle turned upside down as shown in FIG. 1 and a vertex ofthe triangle is a transferring position.

The charging unit 105 is one of the units which sets biascharacteristics in the photoreceptor belt 101. As shown in FIG. 1 andFIG. 2, the charging unit 105 is a unit adopting a non-contact methodand has a charging roller 105A provided close to the photoreceptor belt101 maintaining a prescribed gap (G) that is set. Both ends of a shaft105B of the charging roller 105A in its axial direction are biased by anelastic body 105C like a spring etc. towards the photoreceptor belt 101.A displacement caused by the biasing is regulated by an abutting member105D that includes a film wound around both ends in the axial directionof the charging roller. The abutting member 105D protrudes from theperipheral surface of the charging roller 105A towards the photoreceptorbelt 101.

In the embodiment, the prescribed gap (G) maintained by the abuttingmember 105D is set according to the type of a developer that is used inthe developing unit 107. In the case of the one-component developer thatuses only magnetic toner as developer, the gap is less than or equal to300 μm and in the case of the two-component developer with toner andmagnetic carrier that are mixed, the gap is less than or equal to 500μm. The pushing by the elastic body 105C maintains the gap. Thedifference in the gap is irrespective of the developer that is used, andprevents deterioration of the developing capability when dc and acvoltages are applied.

Direct voltage is applied to the charging roller 105A via the prescribedgap G defined by the abutting member 105D due to constant voltagecontrol of dc −700V through a control circuit (not shown). At the sametime, alternate voltage is applied due to low current control and anaerial discharge is carried out to the photoreceptor belt 101. Thus, thephotoreceptor belt 101 is charged uniformly.

When the photoreceptor belt 101 charged uniformly by the charging unit105 moves, the writing unit 106 carries out optical writing. Anelectrostatic latent image according to either of image information anda paper document image, is formed due to the optical writing. Theelectrostatic latent image is processed to form a visualized image by adeveloper (toner), which is supplied by the developing unit 107. Thevisualized toner image is transferred on a recording paper S that is fedby a paper-feeding unit not shown. The image is transferred on the paperby the transferring unit 108 that includes a transfer roller providedagainst the roller 103 that is at the vertex of the lower part of thetriangle formed by the photoreceptor belt 101. The transferred tonerimage is fixed on the recording paper S by a fixing unit (not shown),and discharged. The cleaning unit 109 removes residual toner andresidual charge on the photoreceptor belt 101, after transferring of theimage. The photoreceptor belt 101 moves again toward the charging unit105, thereby preparing for the next image forming.

The structure of the charging unit 105 is not restricted only to anon-contact roller with respect to the photoreceptor belt 101. Astructure that has a roller in contact with the photoreceptor belt 101,a structure that uses a conductive brush as a charging member, and evena magnetic brush that uses magnetic particles, can be used.

FIG. 3 illustrates a supporting structure of the photoreceptor belt 101.The photoreceptor belt 101 is wound around among the rollers 102 to 104.The roller 102 facing the charging unit is provided with a vibrationabsorber 110 on the surface of the roller 102. The vibration absorber110 uses a strong vibration absorbing material 110A that contains anelastic material like butyl rubber or nitrile rubber.

The structure of the vibration absorber 110 can be varied bysubstituting the vibration absorber provided on the roller 102 by eitherof structures as follows. One of the structures has a strong vibrationabsorbing material 110B in form of a solid block which is press fittedin the hollow cylindrical roller 102 as shown in FIG. 4. The otherstructure has a strong vibration absorbing material 110C in form of ablock with a hollow inside of the block as shown in FIG. 5. In anystructure of the vibration absorber 110, the elastic body made by eitherof butyl rubber and nitrile rubber is used. The vibration absorber 110is provided in either of an axial direction of the roller 102 where theabsorber tends easily to deform by bending and an area around this axialdirection.

Tangent of loss tan δ for any of the strong vibration absorbing material110A or the strong vibration absorbing blocks 110B and 110C, is set tobe greater than or equal to 0.5. The tangent of loss tan δ means atangent of a phase angle δ (loss angle) of stress and strain in thematerial used as the strong vibration absorbing material 110A or thestrong vibration absorbing material blocks 110B and 110C. Value tan δdenotes intrinsic damping effect value of the material, and the greaterthe value of tan δ, the greater the damping effect is. Therefore, in theembodiment, generation of harsh noise is minimized by at least makingthe value of tangent of loss tan δ greater than or equal to 0.5irrespective of use of the strong vibration absorbing material 110A andthe strong vibration absorbing blocks 110B and 110C. The results ofexperiment regarding the settings of loss value tan δ are mentioned inthe latter part.

When dc voltage and in addition ac voltage are applied to the chargingunit 105 as one of the units for setting the bias characteristics, thephotoreceptor belt 101 that corresponds the thin-walled member,resonates due to the vibrating electric field in the charging unit 105.

Since the resonance produced in the photoreceptor belt 101 is reduceddue to absorption of vibrations by the roller 102 that is in contactwith the photoreceptor belt 101, the resonance in the photoreceptor belt101 is suppressed, thereby preventing noise caused by the resonance. Thephotoreceptor belt 101 in particular, which is a thin-walled structure,tends to resonate easily. However, when the photoreceptor belt 101resonates, the resonance is controlled by a vibration absorbing functionof the vibration absorbing material 110A or the vibration absorbingmaterials 110B and 110C which function as vibration absorber 110 whenresonance is produced, there is almost no generation of noise.

As a modification of the structure in the embodiment, a drive roller ofthe photoreceptor belt 101 may be used as a roller provided with thevibration absorber 110. In this case, to transmit the driving force fromthe drive roller to the photoreceptor belt 101, the vibration absorber110 is provided on the drive roller that is in stronger contact with thephotoreceptor belt as compared to the contact of the other roller withthe photoreceptor. By providing the vibration absorber 110 in the driveroller, the resonance produced in the photoreceptor belt 101 can bedealt with in the most effective manner and can be reduced efficiently.

Following is an explanation of another example in which a vibrationabsorption function is provided for the photoreceptor belt 101. FIG. 6illustrates a structure in which the vibration absorber 110 is providedon a supporting plate 111 that is provided on an inner side of thephotoreceptor belt 101. The supporting plate 111 functions as a guidefor the photoreceptor belt 101. The supporting plate 111 is a flat platemade of hard material and the vibration absorber 110 is provided on theside of the supporting plate 111 opposite to the side thereof that facesthe photoreceptor belt 101.

FIG. 7 illustrates a structure in which the charging unit 105 as one ofthe units for setting the bias characteristics in FIG. 6 is disposed ina position opposite to the supporting plate 111 sandwiching thephotoreceptor belt 101. In this case also, the vibration absorber 110 isprovided on the side of the supporting plate 111 opposite to the sidethereof that faces the photoreceptor belt 101.

According to the first embodiment, vibrations generated in the chargingunit 105 when the bias is superimposed with the ac and dc voltagesrespectively by the charging unit 105 are propagated to thephotoreceptor belt 101. When the vibrations are propagated, thephotoreceptor belt 101 starts resonating. By propagating the resonanceto the supporting plate 111 that is in contact with the photoreceptorbelt 101, the vibration absorber 110 absorbs the resonance. Thus, theresonance in the photoreceptor belt 101 is minimized thereby preventingthe generation of noise.

Following is an explanation of a structure in which the photoreceptorbelt 101 itself prevents. FIG. 8 is a cross section of the photoreceptorbelt 101. The photoreceptor belt 101 is structured by superimposing aphotosensitive layer 101B on a surface of a substrate 101A made of athin metal foil or the like. On the opposite side of the photosensitivelayer 101B beyond the substrate 101A is the vibration absorber 110 thatis formed by an elastic body using either of a butyl rubber and nitrilerubber.

The vibration absorber 110 is provided on the side opposite to thephotosensitive layer 110B via the substrate 101A, and thereforevibrations in the photoreceptor belt 101 are minimized due to absorptionby the vibration absorber 110 thereby minimizing resonance in thephotoreceptor belt and preventing the noise.

Why the vibrations are produced in the charging unit 105 has beenexplained above. The cleaning unit 109 provided with the cleaning bladeis a unit that generates vibrations while being in contact with thephotoreceptor belt 101. Vibrations caused by deformation due to scrapingof the cleaning blade and by scraping during restoration of the shapeafter deformation, are also absorbed in the same manner as absorption ofthe resonance produced by the charging unit 105. The image formingapparatus in the invention includes a copying machine, a printer, afacsimile, and a printing machine.

Following is an explanation of still another embodiment of the presentinvention. FIG. 9 is a schematic diagram of an image forming apparatusaccording to another embodiment. An image forming apparatus 20 in FIG. 9is a copying machine in which a thin-walled cylinder is used as a latentimage carrier and plurality of the latent image carriers are provided toallow image formation of plural colors. The image forming apparatus 20in FIG. 9 employs a method of transferring an image of each colorseparation to the same intermediate transfer body one after another andperforming collective transfer of the images superimposed on theintermediate transfer body to a sheet like recording medium such aspaper.

The image forming apparatus 20 includes units as follows. The unitsinclude image forming units 21C, 21Y, 21M, and 21BK that form images ofeach color according to an image on a document. The units also include atransferring unit 22 that is disposed opposite to the image formingunits 21C, 21Y, 21M, and 21 BK. The units further include a manual feedtray 23 and a paper feeding cassette 24 as sheet-like medium feedingunits for feeding a sheet-like recording medium to each transfer areawhere the image forming units 21C, 21Y, 21M, and 21BK and thetransferring unit are disposed opposite to each other. The units furtherinclude register rollers 30 that feed a recording medium according totiming of image forming by the image forming units 21C, 21Y, 21M, and21BK after transferring from the manual feed tray 23 and the paperfeeding cassette 24. The units further include a fixing unit 1 thatcarries out fixing on the recording medium after the image istransferred in the transfer area.

In the image forming apparatus 20, any of sheet-like recording media canbe used as a sheet-like medium. The sheet-like recording medium includesan ordinary paper used for copy in general (hereinafter “ordinarypaper”), an OHP sheet, a 90K paper like a postcard and a card, acardboard of basis weight greater than or equal to 100 g/m² and anenvelope that are so-called special purpose sheets having a heatcapacity more than that of the above types of sheets (hereinafter,simply referred to as “special purpose sheet”).

The image forming units 21C, 21Y, 21M, and 21BK carry out developing ofcyan, yellow, magenta, and black colors respectively. Although the tonercolor handled by each image forming unit is different, the structures ofthe units are the same. Therefore, the structure of the image formingunit 21C, as a representative of the image forming units 21Y, 21M, and21 BK, is explained below with reference to FIG. 10.

The image forming unit 21C has a known structure, which is illustratedin FIG. 10. The unit 21C includes a photoreceptor drum 25C as anelectrostatic latent image carrier, and also a charging unit 27C, adeveloping unit 26C, and a cleaning unit 28C that are disposed aroundthe drum 25C in this order along the rotational direction F of the drum25C. Further, writing light is received between the charging unit 27Cand the developing unit 26C. The image forming apparatus 20 in FIG. 9has the transferring unit 22 that is extended in a slanting direction,and therefore the transferring unit 22 occupies less space as comparedto the space occupied by the transferring unit 22 provided in ahorizontal direction.

The charging unit 27C includes, as shown in FIG. 10, of a roller havingthe structure similar to that in FIG. 2. Abutting members that protrudetowards the photoreceptor drum 25C are provided on both ends of theroller in the axial direction to set a prescribed gap between thephotoreceptor drum 25C and the roller of the charging unit 27C. Theprescribed gap is explained later.

The developing unit 26C uses a biaxial agitation method carried out byagitating screws 26C1 and 26C2 which are two agitators that carry outmixing and agitating of toner supplied from a toner cartridge withmagnetic carrier. Developer is frictionally charged due to agitation andmagnetic carrier toner is adhered to the developer. The developer iscarried on a surface of a developing sleeve 26C3 as a developer carrier,and is provided with a magnetic roller that has north and south poleslined up inside. The developer is supplied toward the photoreceptor 25Cafter a layer thickness is regulated by a doctor blade 26C4.

The developing sleeve 26C3 in the developing unit 26C is disposed to seta prescribed gap from the photoreceptor drum 25C. In the structure shownin FIG. 10, the prescribed gap is set to be less than or equal to 500μm, preferably to 470 μm. This prescribed gap is set to allow thecapability of toner adhesion to an electrostatic latent image on thephotoreceptor drum to be enhanced, the developing capability ofcontinuous black image to be improved, and uniform and identicaldevelopment with utmost clarity of fine lines such as characters anddots etc to be realized. It is possible to maintain uniform and highdeveloping capability of toner dots by giving identical reproducibilityto the electrostatic latent image by setting the gap less than or equalto 500 μm. Making the prescribed gap greater than 500 μm does notguarantee good capability.

The abutting members (not shown) provided on both ends of the developingsleeve 26C3 in the axial direction are used for setting the gap betweenthe developing sleeve 26C3 and the photoreceptor drum 25C. The abuttingmember is a member protruding toward the photoreceptor drum 25C that issimilar to the abutting member 105D in the charging unit 105 shown inFIG. 2. In the embodiment, an abutting roller is used. The protrudingroller is larger than the photoreceptor drum 25C and has an outerdiameter equivalent to an amount of protruding more than the prescribedgap.

The structure in which the prescribed gap is set, enables to carry outsplashing of toner to an image area on the latent image carrier andreturning of toner from non-image area to the developer carrier due tothe bias characteristics according to the type of developer used inefficient manner. This can optimize the electrical field effect by thebias and reliably prevent deterioration of developing capability andproduction of resonance in the latent image carrier.

The developing sleeve 26C3 maintains the gap of 470 μm from thephotoreceptor drum 25C and carries a developer that includes toner andcarrier made of the magnetic material. A negatively charged developingbias supplied from a power supply (not shown) is applied to thedeveloping sleeve 26C3. Negatively charged toner is splashed and appliedon an area of exposure of the photoreceptor drum 25C based on anelectric field created between the sleeve 16C3 and the drum 25C, therebycarrying out developing. Thus, a toner image is formed.

The developing bias to be used includes a first electric potential areaV1 and a second electric potential area V2 generated by superposing acvoltage on dc voltage as shown in FIG. 47. The first electric potentialarea V1 in which toner is moved from the developing sleeve 26C3 to thephotoreceptor drum 25C, and the second electric potential area V2 inwhich toner is moved from the photoreceptor drum 25C to the developingsleeve 26C3. The negatively charged toner in the brush-like developer onthe surface of the developing sleeve 26C3 is adhered, due to anelectrostatic force, to an area of electrostatic latent image on thephotoreceptor 25 by the developing bias.

At this time, an electrostatic force is produced so that a positivelycharged carrier is moved to an area of non-electrostatic latent image onthe photoreceptor 25. However, due to restraining of carrier by amagnetic force of a magnetic roll in a developing roller 26C1, thepositively charged carrier is not moved on to the photoreceptor drum25C. Using of such a type of developing bias improves capability oftoner deposition on the electrostatic latent image on the photoreceptordrum 25C, improves developing capability of continuous black image, andenables uniform developing with utmost clarity of fine lines such ascharacters and dots etc. identical to the electrostatic latent image.

In FIG. 10, a process cartridge is structured by supporting at least onefrom among the charging unit 27C which sets the bias characteristics tothe photoreceptor drum 25C, the developing unit 26C, and the cleaningunit 28C having a cleaning blade 28C1 that is in contact with thephotoreceptor drum 25C, by the same support as that of the photoreceptordrum 25C. The process cartridge is detachable from the main body of theimage forming apparatus. Moreover, image forming units for four colorscan be collectively drawn out to an outer side.

The cleaning unit is provided not only for the photoreceptor drum 25C.In addition, a cleaning unit 27C1 is provided for cleaning a roller usedin the charging unit 27C. The cleaning unit 27C1 eliminates foreignmatters like dust and toner reversely transferred from the photoreceptordrum 25C to the charging unit 27C, thereby preventing variation in theelectric field due to charging unevenness and carrying out stable anduniform charging.

On the other hand, the photoreceptor drum 25C is a cylinder of 0.75millimeter thick metal with a photosensitive layer provided on thesurface of the cylinder and a vibration absorber provided inside thecylinder.

FIG. 11 and FIG. 12 illustrate the internal structure of thephotoreceptor drum 25C. The vibration absorber (shown by referencenumeral 110′ and 110″ for convenience) that is formed by an elasticmaterial containing either of butyl rubber and nitrile rubber is fittedinside the photoreceptor drum 25C. The vibration absorber shown 110′ inFIG. 11 is in the form of a solid cylinder and the vibration absorber110″ shown in FIG. 12 is in the form of a hollow cylinder. It is notedthat the vibration absorber 110′ explained hereinafter includes thevibration absorber 110″ when the two absorbers do not need to beindividually explained. The vibration absorber 110′ is provided ineither of an area of the roller 102 in its axial direction where theroller tends to easily deform by bending and a region around this area.

The tangent of loss tan δ of the vibration absorber 110′ is set to begreater than or equal to 0.5 for the following reason. The tangent ofloss tan δ means a tangent of phase angle δ (loss angle) of stress andstrain in the material to be used in the vibration absorber, and thegreater the value of tan δ, the greater the damping effect is.

Following is a result of experiment carried out for measurement of thetangent of loss tan δ, and the measurement was carried out according toa non-resonant vibration method that is prescribed in the JapaneseIndustrial Standards (JIS) K7244-4. A sample having a thickness of 2millimeters, a width of 5 millimeters, and a length of 30 millimeterswas used as a specimen and a result was achieved by carrying outmeasurement at applying frequency of 30 Hertz. The solid cylinder asshown in FIG. 11 and the hollow cylinder as shown in FIG. 12 which havedifferent values of tangent of loss tan δ were prepared for samples forthe experiment.

FIG. 13 is graphical representation of results of the experiment.Acoustic power is on a vertical axis and the tangent of loss tan δ is ona horizontal axis in this figure. It is evident from the result of theexperiment that vibrations were reduced to a satisfactory level ofhearing (high frequency sound is not harsh to ears) when the value oftan δ is 0.5 or more in the solid cylindrical vibration absorber 110′ ofFIG. 11. Similarly, vibrations were reduced to a satisfactory level ofhearing when the value of tan δ is 0.6 or more in the hollow cylindricalvibration absorber 110″ of FIG. 12. Moreover, even stronger vibrationreduction effect can be achieved when the value of tan δ is 0.8 or more.Apart from noise due to the developing unit, noise due to the chargingunit and cleaning blades was also measured together during theexperiment.

From these results, practically satisfactory damping effect can beachieved by setting the tangent of loss tan δ to 0.5 or more and evenbetter damping effect can be achieved when the value of tangent of losstan δ is set to 0.8 or more. Thus, resonance (noise) produced in thedeveloping unit 26, the charging unit 27, and the cleaning blade can bereduced. The structure of the vibration absorber 110′ in thephotoreceptor drum 25C is not limited to the photoreceptor drum 25C thatforms an image of cyan color only, but the same structure can be used inthe other photoreceptor drums as well.

The tangent of loss tan δ of the solid cylindrical vibration absorber110′ of FIG. 11 is smaller than the tangent of loss tan δ of the hollowcylindrical vibration absorber 110″ of FIG. 12 because of the differencein masses of the two vibration absorbers 110′ and 110″. The harsh noisecan be reduced effectively by changing the resonating frequency of thephotoreceptor drum to the low frequency. The hollow cylinder is afavorable from the material cost point of view since this cylinder usesless amount of material than the solid cylinder.

The vibration absorber 110′ is integrated into the photoreceptor drum25C by either of press fitting and bonding. Assume that an innerdiameter of the photoreceptor drum is D and an outer diameter of thevibration absorber 110′ is d. If the vibration absorber 110′ is pressfitted and d is less than D, then damping effect and noise reductioneffect cannot be achieved because the vibration absorber is not fittedtightly to the inner surface of the photoreceptor. Conversely, if d isexcessively greater than D, excessive force is required for fixing thedamper inside the photoreceptor. This creates difficulties in assemblingand may result in deformation of the photoreceptor while assembling.Therefore, it is preferable that a relation between D and d is in arange of D≦d≦(D+1) mm.

Following is an explanation of the photoreceptor drum in which thevibration absorber 110′ is inserted. As a photoreceptor used in imageprocessing based on the electrophotographic method, one that uses aninorganic semiconductor material like selenium or amorphous silicon,etc., one that uses an organic semiconductor material, and one as acombination of the two are known. In recent years, the organicphotoconductors (photoreceptors) (OPC) have been used widely due totheir low cost, a high degree of flexibility in designing, andnon-polluting nature.

As the organic photoreceptor used in electrophotography, those asfollows are known photoreceptors. That is, the organic photoreceptorincludes a photoreceptor of photoconductive resins represented bypolyvinyl carbazole (PVK), a charge transfer complex type photoreceptorrepresented by PVK-TNF (2,4,7-trinitrofluorenone), a pigment dispersingtype photoreceptor represented by phthalocyanine binder, and a functionseparated type photoreceptor used as a combination of charge generatingmaterial and charge carrying material. Especially, the functionseparated type photoreceptors have been focused on. The mechanism in theelectrostatic latent image forming in the function separated typephotoreceptors is as follows. When light is irradiated after thephotoreceptor is charged, the light passes through a transparent chargecarrying layer, and is absorbed by the charge generating material in thecharge generating layer. The charge generating material that hasabsorbed the light generates charge carriers and these charge carriersare injected into the charge carrying layer. The charge carriers moveinside the charge carrying layer according to an electric fieldgenerated by charging and an electrostatic latent image is formed due toneutralization of charge on the surface of the photoreceptor.

In the function separated type photoreceptors, it is known and useful touse a combination of the charge carrying material that absorbs lightmainly in an ultraviolet region with the charge generating material thatabsorbs light mainly in a visible region.

However, the organic-based electrophotographic photoreceptors have poormechanical and chemical durability, which is a known shortcoming. Mostof the charge carrying materials is developed as low molecularcompounds. However, the low molecular compounds do not have a capacityto form a membrane independently. Therefore, the compounds are dispersedinto or mixed with inactive high molecules to be used. Generally, thecharge carrying layer, including the low molecular charge carryingmaterial and inactive high molecules, is soft and has poor mechanicaldurability. In the electrophotography process, mechanical load exertedby various parts coming in contact (developing unit, charging unit,transfer paper, cleaning brush, cleaning blade etc.) tends to break themembrane easily.

Therefore, a protective layer that contains filler to protect aphotosensitive layer and to improve the durability of the photosensitivelayer is also provided on the photosensitive layer as a top layer. Amaterial used for the protective layer includes resins such as ABSresin, ACS resin, olefin vinyl monomer copolymer, chlorinated polyetherresin, allyl resin, phenolic resin, polyacetal resin, polyamide resin,polyamide imide resin, polyacrylate resin, polyallyl sulfone resin,polybutylene resin, polybutylene terephthalate resin, polycarbonateresin, polyether sulfone resin, polyethine resin, polyetheleneterephthalate resin, polyimide resin, acrylic resin, polymethale pentaneresin, polypropylene resin, polyphenylene oxide resin, polysulfoneresin, AS resin, AB resin, BS resin, polyurethane resin, polyvinylchloride resin, polyvinyledene chloride resin, and epoxy resin. A fillerto be added to further improve the wear resistance of the protectivelayer includes fluororesin like polytetra fluoroethylene, and siliconresin, and these resins dispersed with inorganic materials like titaniumoxide, tin oxide, potassium titanate, silica, alumina, etc.

Quantity of the filler to be added to the protective layer by weight isnormally in a range of 10% to 40%, preferably in a range of 20% to 30%.When the quantity of the filler is less than 10%, the wear is increased,which deteriorates the durability. When the quantity of the filler ismore than 40%, rise in electric potential in a bright area duringexposure is increased and photographic sensitivity drops to the extentthat cannot be neglected, hence more than 40% is not desirable.Moreover, dispersion-assisting agent can be added to the protectivelayer to improve dispersion of the filler. A dispersion-assisting agentused in paints can be used for adding. Normally, the quantity of thedispersion-assisting agent with respect to the quantity of the fillercontained is in a range of 0.5% to 4%, preferably in a range of 1% to2%. Furthermore, adding of charge carrying material to the protectivelayer is also effective and an antioxidant can also be added ifnecessary. A method of forming the protective layer includes a normalcoating method like a spraying method.

The thickness of the protective layer is in a range of 0.5 μm to 10 μm,preferably in a range of about 4 μm to 6 μm. An intermediate layer canbe provided between the photosensitive layer and the protective layer ofthe photoreceptor used in the embodiment. Normally, a binder resin isused as a main component in the intermediate layer. The resins for thebinder or the like include polyamide, alcohol-soluble nylon,water-soluble polyvinyl butyral, polyvinyl buteral, or polyvinylalcohol. A method of forming the intermediate layer includes the normalcoating method. The appropriate thickness of the intermediate layer isin a range of about 0.05 μm to 2 μm.

The inventors of the present invention carried out an experiment on thenoise reduction effect when the vibration absorber was fitted inside thephotoreceptor having the above structure, and the following result wasobtained. Following is an explanation about the photoreceptor that isused in this experiment.

A photoreceptor for evaluation is similar to the one explained in theprevious embodiment that employs a hollow cylinder having an outerdiameter of 30 millimeters, an inner diameter of 28.5 millimeters, and awall thickness of 0.75 millimeter.

(1) Making of Photoreceptor (No. 1) for Evaluation

Solutions of compositions given below were sequentially coated on analuminum drum having an outer diameter φ30 millimeters and dried. Thesolutions include a coating solution for undercoat layer, a coatingsolution for charge generating layer, and a coating solution for chargecarrying layer. When the coated layers were dried, the undercoat layerof thickness 3.5 μm, the charge generating layer of thickness 0.2 μm,and the charge carrying layer of thickness 25 μm were formed. Thus,electrophotographic photoreceptor (photoreceptor No. 1) for evaluationwas obtained.

Coating Solution for Undercoat Layer:

Alkyd resin: 6 weight parts (Bekkozol 1307-60-EL made by DAINIPPON INK &CHEMICALS INDUSTRIES)

Melamine resin: 4 weight parts (Super Bekkamine G-821-60 made byDAINIPPON INK & CHEMICALS INDUSTRIES)

Titanium oxide: 40 weight parts

Methyl ethyl ketone: 200 weight parts

Coating Solution for Charge Generating Layer:

Trisazo pigments with the formulation as shown in chemical formula 1:2.5 weight parts

Polyvinyl butyral (UCC: XYHL): 0.25 weight parts

cyclohexanone: 200 weight parts

methyl ethyl ketone: 80 weight parts

Coating Solution for Charge Carrying Layer:

Bisphenol A-type polycarbonate: 10 weight parts (Panlite K1300 made byTEIJIN)

Low molecular charge carrying material with the formulation as shown inchemical formula 2: 10 weight parts

Methylene chloride: 100 weight parts

(2) Making of Photoreceptor (No. 2) for Evaluation

The photoreceptor (No. 2) for evaluation was made by forming aprotective layer with a thickness of 2 μm on the charge carrying layerof the photoreceptor (No. 1) using a coating solution for protectivelayer with the formulation given below. The remaining layers of thephotoreceptor (No. 2) were the same as in the photoreceptor (No. 1).

Coating Solution for Protective Layer:

Charge carrying material with the formulation as shown in chemicalformula 3: 2 weight parts

A-type polycarbonate: 4 weight parts

Methylene chloride: 100 weight parts

(3) Making of Photoreceptor (No. 3) for Evaluation

The photoreceptor (No. 3) for evaluation was made by forming aprotective layer with a thickness of 2 μm on the charge carrying layerof the photoreceptor (No. 1) using a coating solution for protectivelayer with the formulation shown in chemical formula 3. The remaininglayers of the photoreceptor (No. 3) were the same as in thephotoreceptor (No. 1).

Coating Solution for Protective Layer:

Charge carrying material with the formulation as shown in chemicalformula 3: 4 weight parts

A-type polycarbonate: 4 weight parts

Titanium oxide: 1 weight part

Methylene chloride: 100 weight parts

(4) Making of Photoreceptor (No. 4) for Evaluation.

The photoreceptor (No. 4) for evaluation was made by substitutingtitanium oxide for a filler which was dispersed in the protective layerof the photoreceptor (No. 3), by aluminum oxide. The remaining layers ofthe photoreceptor (No. 4) were the same as in the photoreceptor (No. 3).

The inventors of the present invention achieved following results bycarrying out experiments using the photoreceptors for evaluation No. 1to No. 4. The experiments were carried out on quality of images on eachof the photoreceptors and on noise caused by the case where thevibration absorber was fitted in the photoreceptor.

In the experiments, a continuous paper-feeding test was carried out witha digital copying machine IMAGIO MF 200 (trade name) made by RICOHCOMPANY, LTD. The image quality (overall evaluation of image density,resolution etc.) was found to be very good. A F-to-C ratio betweenmolecules of fluorine and carbon on the surface of the photoreceptor asan index for deposition of fluorine-based material existing on thesurface of the photoreceptor was found to be zero. Moreover, duringrunning of the copying machine, the amount of decrease Δd from aninitial value in the thickness of the photosensitive layer was found tobe appropriate and hard copies having high definition could be obtainedwith stability during long period of time.

In the photoreceptors No. 1 to No. 4, the vibration absorber 110′ wasfitted as shown in FIG. 11 and FIG. 12 and developing bias in which acvoltage was superimposed on dc voltage was applied to thephotoreceptors. As a result, resonance in the photoreceptors wasreduced, transmission of vibrations of a cleaning blade was prevented,and prevention of noise generation was confirmed.

Following is an explanation of practical application of the presentinvention.

FIG. 14 illustrates a laser printer as an example of the image formingapparatus that uses a one-component developer using magnetic toner as adeveloper. In a case of using the one component developer, structure ofa basic image forming section resembles to that of an image formingapparatus that uses a two-component developer.

In FIG. 14, reference numeral 50 is an image carrier in the form of adrum (hereinafter “photoreceptor drum”) provided inside the main body ofthe printer. Right side of the figure is a front side of the printer.When the printer is in use, the photoreceptor drum 50 rotates in adirection of an arrow shown in the figure (in counterclockwisedirection). To start with, a charging roller 51 charges the surface ofthe photoreceptor drum 50 uniformly and then writing is carried out byirradiating laser light L from an optical writing unit thereby formingan electrostatic latent image on the surface of the photoreceptor drum50.

A developing unit 52 provided adjacent to the photoreceptor drum 50includes a developing roller 53. A prescribed gap between thephotoreceptor drum 50 and the developing roller 53 is set to 300 μm orless, preferably 280 μm. The one-component developer stored in adeveloper storage 68 is carried on the surface of the developing roller53 and is supplied to the photoreceptor drum. The prescribed gap is setto prevent deterioration of developing capability when dc voltage isapplied and further ac voltage is applied in addition, similar to thecase of using the two-component developer. When this gap is excessivelylarge and the developing roller 53 is farther away from thephotoreceptor drum 50, the improvement in the developing capacity whenthe ac voltage image is superimposed on the dc voltage, is affected.When the gap is set to be less than 300 μm i.e. to be made narrow, it ispossible to further improve the high developing capacity such that adeveloped image is identical to a latent image having utmost clarity andtoner dots are uniform. To maintain this prescribed gap, an abuttingroller is used like in the case of the developing sleeve 26C3 as shownin FIG. 10.

To adhere magnetic toner as the one-component developer to thephotoreceptor drum 50, a developing bias having dc voltage superimposedby ac voltage on it by a power source not shown is applied to thedeveloping roller 53 in addition to an electrostatic absorption force ofan electrostatic latent image formed on the surface of the photoreceptordrum 50 are applied combined on the developing roller 53. The magnetictoner is supplied to the photoreceptor drum 50 by the developing roller53 in the developing unit 52 through rotation of the photoreceptor drum50 to develop an electrostatic latent image on the photoreceptor drum50.

The developing unit 52 includes known components such as a developingblade 54 that scrapes the developing roller 53 thereby carrying outfrictional charging to toner, an agitating shaft 55 and an agitator 56that agitate and carry the toner, and a toner ending sensor 57 thatdetects the quantity of the toner remaining in the developing unit.

In the structure shown in FIG. 14, a vibration absorber is included inthe photoreceptor drum 50 similarly as shown in FIG. 10. For thestructure, the structures shown in FIG. 11 and FIG. 12 are used.

In FIG. 14, a sheet-like recording material which is stored in apaper-feeding cassette (not shown) is fed along the rotation of thephotoreceptor drum 50, and the recording material stops for a time whenit is held between a pair of register rollers 59. When the pair ofregister rollers 59 rotates with the timing matched with that of animage on the photoreceptor drum 50, the recording material is guided bya part 70A on an outer surface of a cartridge case 70 and forwarded to atransfer nip between the photoreceptor drum 50 and the transfer roller60. A toner image on the photoreceptor drum 50 is transferred to therecording material through a transfer bias from the transfer roller 60.

After transferring of the image to the recording material, the recordingmaterial is decharged by a decharging pin 61 and carried upward througha carrier path in a state of the material as indicated by a referencenumeral S. The recording material is then guided to a fixing nip formedat a position where a pressure roller and a fixing roller of the fixingunit not shown are in contact with each other. Here, the transferredimage is fixed by heat and pressure, and the recording material isdischarged to a paper discharging section with an image surface facingdownward.

Residual toner on the photoreceptor drum 50 after having transferred theimage is eliminated by a cleaning blade 58 of the cleaning unit 57through the rotation of the photoreceptor drum 50. The photoreceptordrum 50 is kept ready for recharging by the charging roller 51.

In the laser printer structured as shown in FIG. 14, the photoreceptordrum 50, the charging roller 51, the developing unit 52, and thecleaning unit 57 etc., are accommodated in the cartridge case 70 as acasing of the printer, thereby forming a process cartridge 71. The mainbody of the image forming apparatus is made compact in size by improvingan accuracy of relative position of each component with respect to theother component. The handling is made easier by enabling the replacementof parts at a time instead of replacing them at different times. Themaintenance of the image forming apparatus is made simple to make itslife longer.

Thus, according to the first embodiment, the vibration absorber isdisposed on the side opposite to the surface facing the unit in whichthe bias characteristics are set in the latent image carrier. Therefore,due to the bias characteristics, the vibration absorber that is incontact with the latent image carrier absorbs a part of the vibrationsin the latent image carrier, which is caused by the vibrating electricfield generated when ac voltage is applied. This enables to reduce theresonance of the latent image carrier, thereby preventing noise. Even ifthe latent image carrier is either of a belt and a thin-walled cylinder,noise can be prevented without increasing the mass and complicating thestructure of the latent image carrier.

Further, since the vibration absorber is in the form of a roller and thestrong vibration absorbing material is provided either on the surface ofthe absorber or inside the absorber, the propagation of vibrations isprevented when the roller is in contact with the latent image carrier.Thus, the noise due to resonance in the latent image carrier isprevented.

Moreover, since the drive roller is used as the vibration absorber whenthe latent image carrier is in the form of a belt, a material that comesin firm contact with the latent image carrier, can be used as a damper.This facilitates the absorption of vibrations generated in the latentimage carrier and enables to reduce the resonance in the latent imagecarrier by using the existing structure.

When the latent image carrier is a belt, the vibration absorber isprovided on the opposite side of the surface of the supporting platewhere the supporting plate is in contact with the latent image carrier.The supporting plate is made of a rigid body in the form of a flat platethat is in contact with the belt. Therefore, the vibration absorberabsorbs the vibrations generated in the belt without obstructing themovement, and resonance produced in the latent image carrier can bereduced.

Since the vibration absorber is disposed in a position opposite to theunit in which the bias characteristics with respect to the latent imagecarrier are set, the resonance can be reduced in the most effectivemanner at the origin of resonance produced in the latent image carrierdue to the bias characteristics.

Since the latent image carrier is a substrate in the form of a thin beltmade of a material that absorbs strong vibrations, the material canreduce the vibrations of the latent image carrier as compared to thecase where a photosensitive layer is provided on the surface of the thinbelt-like substrate. Therefore, there is no need to have a specialarrangement for damping and hence no extra cost is needed.

By setting the value of tangent of loss tan δ which affects the dampingeffect to a value greater than or equal to 0.5, the frequency ofresonance can be varied to the frequency range in which high frequencysound that is harsh to ears is not generated. Therefore, even when thenoise is generated from the latent image carrier, the same effect asthat of reducing the noise can be achieved.

Since the vibration absorber is in the solid cylindrical form, it ispossible to vary the resonance frequency of the latent image carrier tothe low frequency range efficiently by using the difference of masscompared to that of the hollow cylindrical form. Thus, the resonancecaused by the vibrations of the latent image carrier can be preventedand noise can be reduced in an efficient manner.

It is possible to reduce the material cost by using the vibrationabsorber in the hollow cylindrical form. In a case of the structure thatleads to the reduction in the material cost, in other words, even in acase where it is difficult to decrease the resonance frequency due tothe mass different from that in a case of the solid cylindrical form,deterioration of the damping effect can be prevented reliably by settingthe value of tangent of loss tan δ which affects the damping effect to avalue greater than or equal to 0.6.

Moreover, since the vibration absorber is fitted inside the latent imagecarrier by either of press fitting and bonding, it is thoroughlyintegrated with the latent image carrier thereby reducing the resonancein the latent image carrier in an efficient manner.

A second embodiment of this invention will be explained below.

FIG. 15 is a cross section of a schematic structure of an image formingapparatus that uses an image carrier drum in the form of a hollowcylinder according to the second embodiment. An image carrier drum 202in the figure is a photoreceptor drum with a photosensitive layerprovided on an outer peripheral surface of a circular cylindrical tubemade of a conductive metal like aluminum. In an example shown in FIG.15, an image forming module 218 is structured by assembling the imagecarrier drum 202 integrally with an image forming unit that forms atoner image as explained later. The image carrier drum 202 is rotatablysupported by a case 219 of the image forming module 218, and is drivenby a drive motor (not shown) in the clockwise direction in FIG. 15. Atthis time, a charging roller 220 as an example of a charging unitrotatably supported by the case 219 is rotated, and a charging voltageis applied to the charging roller 220. Thereby, the surface of the imagecarrier drum 202 is charged to a prescribed polarity. In this imageforming apparatus, a spacer including a tape 201 is wound around eachend of the charging roller 220 in its longitudinal direction. The tape201 is in contact with the outer peripheral surface of the image carrierdrum 202 and the charging roller 220 is in a position such that there isa minute gap with respect to the surface of the image carrier drum 202.

A modulated laser beam L emitted from an exposing unit (not shown) isirradiated on the surface of the image carrier drum after charging, andan electrostatic latent image is formed on the image carrier drum. It isnoted that the exposing unit is provided separately apart from the imageforming module 218. This electrostatic latent image is visualized as atoner image by a developing unit 222. The toner image is carried on atransfer belt 208 and is transferred to a recording medium P like atransfer paper etc. that travels in a direction of an arrow A by anaction of a transfer brush 209. The transfer brush 209 is an example ofa transferring unit. When the toner image having been transferred to therecording medium P passes through a fixing unit (not shown), the tonerimage is fixed on the recording medium P due to effect of heat andpressure. A residual toner on the image carrier drum that is left afterthe transferring of the toner image is eliminated by combined action ofa cleaning brush 229 and a cleaning blade 230 of a cleaning unit 227.

The developing unit 222 includes a developing case 223 formed with apart of the case 219 of the image forming module 218, and a developingroller 224 rotatably supported by the developing case 223. Thedeveloping case 223 contains developer D. The rotating developing roller224 carries the developer D and transfers it. The transferred developervisualizes the electrostatic latent image. In this case, thetwo-component developer including toner and carrier, is used. When adecrease in toner density of the developer is detected, the developingcase 223 is replenished with the toner from a toner container 233. Thecleaning unit 227 includes a cleaning case 228 also formed with a partof the case 219 of the image forming module 218. The cleaning brush 229and the cleaning blade 230 are supported by the cleaning case 228. Thus,in the image forming apparatus shown in FIG. 15, the image carrier drum202 and the image forming units, arranged around the drum, such as thecharging roller 220, the developing roller 224, the cleaning brush 229,and the cleaning blade 230 are integrally assembled to the case 219 toform the image forming module 218. The image forming module 218 isdetachable from the casing (not shown) of the image forming apparatusand can be replaced by a new image forming module when the modulereaches end of its life.

Thus, in the image forming apparatus, the toner image is formed on thesurface of the rotating image carrier drum 202, and the formed tonerimage is then transferred to the recording medium P to achieve arecorded image. The fixing unit fixes the toner image that has beentransferred on the recording medium P. The toner having a low meltingpoint is used in the developing unit to enable the fixing of the tonerimage in the fixing unit at a comparatively low surface temperature of afixing roller, for example, 145° C. The image forming apparatus forms atoner image on the image carrier drum using toner having an outflowstart temperature, measured by flow tester method, of less than or equalto 102° C., preferably in a range of 99° C. to 102° C. A Shimadzu FlowTester CFT500 made by SHIMADZU SEISAKUSHO is used for measurement of theoutflow start temperature by the flow tester method.

This flow tester is provided to melt a test sample in a cylinder byheating the cylinder from outside, apply pressure with a constant loadby a piston from the topside of the cylinder, and extrude the testsample through pores in a die disposed at a bottom of the cylinder. Atemperature at which the melted test sample starts extruding from thepores of the die is an outflow start temperature. By using toner havingan outflow start temperature less than or equal to 102° C., the tonerimage is formed on the image carrier drum. Specifically, the toner isused under setting conditions as follows, load exerted on the piston: 10kg/cm², temperature rising rate: 3.0° C./min, diameter of pore in thedie: 0.5 millimeter, and die length: 10 millimeters. The flow testermethod is described in Japanese Patent Application Laid OpenPublications No. 2001-147551 and No. 2001-75106.

The charging roller 220 is disposed on the outer peripheral surface ofthe image carrier drum 202 in FIG. 15 and the cleaning blade 230 is incontact with the surface of the drum. When charging voltage having acvoltage superimposed on dc voltage is applied to the charging roller220, the charging roller 220 vibrates due to the application of the acvoltage. Further, the cleaning blade 230 vibrates due to stick-slipduring rotation of the image carrier drum 202. These vibrationstransmitted to the image carrier drum 202 may cause the drum 202 tovibrate and lead to generation of noise. Especially, when the tonerhaving a low melting point is used, a large amount of noise may begenerated in the conventional image forming apparatus thereby causingthe user to feel uncomfortable. As a tube of the image carrier drum 202,a thin-walled hollow cylinder made of aluminum is used. This tube has anouter diameter of about 30 millimeters, an inner diameter of about 28.5millimeters, and a wall thickness of about 0.75 millimeter. Theconventional image forming apparatus tends to generate noise easily whenthe image carrier drum 202 formed of such a thin tube is used.

Therefore, a damper 204 is provided inside the image carrier drum 202 inthe image forming apparatus as shown in FIG. 15 and FIG. 16. The damper204 shown in FIG. 17 can also be used. The damper 204 is formed of amaterial having a tangent of loss tan δ greater than or equal to 0.5.The tangent of loss tan δ is a tangent of a phase angle δ (loss angle)of stress and strain in the material. The greater the value of tangentof loss tan δ, the greater the damping effect is.

In the image forming apparatus, considering the characteristics of thistype of damping material, the damper 204 made of the material having atangent of loss tan δ greater than or equal to 0.5 is provided toeffectively suppress vibrations of the rotating image carrier drum 202.Even by using the toner having a low melting point, it is possible toreduce the noise generated in the image carrier drum 202 during imageformation to an extremely low level. A rubber material like butylrubber, nitrile rubber etc. can be used as a material having the tangentof loss tan δ greater than or equal to 0.5.

The inventors of the present invention provided the damper 204 made ofrubber as shown in FIG. 17 having a value of the tangent of loss tan δ0.5 and the damper 204 made of ABS resin having a value of the tangentof loss tan δ less than 0.5 inside the image carrier drum 202respectively as shown in FIG. 15, and carried out image forming to findout if the noise was audible to a person who was present in the vicinityof the image forming apparatus. The charging voltage in which an acvoltage was superimposed on dc voltage was applied on the chargingroller 220. The inventors used two types of toner. One of the toners hadan outflow start temperature of 102° C. or less and had a low meltingpoint such that the toner image could be fixed at a surface temperatureof the fixing roller of about 145° C. in the experimental apparatus. Theother toner had the outflow start temperature of higher than 102° C. anda high melting point such that the toner image could be fixed at asurface temperature of the fixing roller of about 175° C. The tangent ofloss tan δ of the damper 204 was measured according to a non-resonantvibration method prescribed in JIS K7244-4. A specimen having athickness of 2 millimeters, a width of 5 millimeters, and a length of 30millimeters was used, and measurement was carried out at appliedfrequency of 30 Hertz. The results of the experiment are shown intable 1. TABLE 1 Toner having a high Toner having a low melting pointmelting point Damper made of ABS No generation of Generation of noiseresin noise Damper made of No generation of No generation of noiserubber having tan δ 0.5 noise

In table 1, “generation of noise” means that the person observing theexperiment being in the vicinity of the image forming apparatus couldclearly hear the noise, and “no generation of noise” means that thenoise was not heard. As can be seen in table 1, even with the tonerhaving the low melting point, when the damper 204 made of a materialthat had the tangent of loss tan δ 0.5 was inserted inside the imagecarrier drum 202, generation of noise was not noticed. With the sametoner, when the damper 204 made of a material that had the tangent ofloss tan δ less than 0.5, generation of noise was confirmed. When thesame experiment was carried out without inserting the damper inside theimage carrier drum, significant noise generation was recognized by usingeither of the toners.

When the damper 204 is formed of a material that has the tangent of losstan δ greater than 0.5, particularly 0.6 or more, or even 0.8 or more,the damping effect to the image carrier drum 202 can be improvedconsiderably.

When a toner including a metallic salt of high fatty acid like a zincstearate is used as a toner for the image forming apparatus, a part ofthe toner gets deposited on the surface of the image carrier drum 202.Due to the toner deposited on the surface, the coefficient of frictionof the toner with the cleaning blade decreases thereby improving slip ofan edge of the cleaning blade 230. This reduces vibrations in thecleaning blade and further improves the effect of preventing noisegeneration.

The damper 204 in FIG. 16 is in a solid circular cylindrical formwhereas the damper 204 in FIG. 17 is in a hollow circular cylindricalform. When the solid damper 204 as shown in FIG. 16 is used, the weightof the damper 204 is increased, and thereby the overall weight of theassembly of the damper 204 and the image carrier drum 202 increases.Thus, high frequency noise that is harsh to ears can be reducedeffectively. On the other hand, when the hollow damper 204 as shown inFIG. 17 is used, the material used for the damper can be reduced and thecost can be also reduced. In such a case, the tangent of loss tan δ, theweight, the form, especially the thickness of the damper 204 has to beset appropriately to obtain required damping effect. It is possible touse the damper 204 molded in a hollow circular cylindrical form, and itis also possible to structure the damper 204 in the hollow circularcylindrical form by rolling up the sheet-like material. According to thelatter method, the damper 204 in the hollow circular cylindrical formcan be fabricated at a low cost using the sheet-like material therebyreducing the cost considerably.

As a method of fixing the damper 204 into the image carrier drum 202,methods as follows can be employed. One of the methods is realized byinserting, by press fitting, a damper into the image carrier drum 202.More specifically, the damper has a setting such that d is slightlylarger than D where d is an outer diameter of the damper 204 beforebeing inserted into the image carrier drum 202 and D is an innerdiameter of the image carrier drum 202. Another method is realized bysetting d to be slightly smaller than D, inserting such a damper 204into the image carrier drum 202, and fixing the damper 204 to the innerwall surface of the image carrier drum 202 with an adhesive. Sufficientdamping effect can be achieved by using either of the methods. However,in the case of press fitting the damper inside the image carrier drum,if d is smaller than D, then the damper 204 is not fitted tightlyagainst the inner wall surface of the image carrier drum 202 therebydeteriorating the damping effect. Conversely, if d is excessively largerthan D, excessive force is required for inserting the damper 204 intothe image carrier drum 202. This not only creates difficulties inassembling but also results in deformation of the image carrier drumduring assembling. Therefore, it is preferable to have a relationbetween values of D and d such that D≦d≦(D+1) millimeter.

When the damper is fixed inside the image carrier drum by press fitting,there is no need to use an adhesive and the cost for this fixing can bereduced. Besides, the damper 204 can be removed from the image carrierdrum 202 easily and can be recycled. Whereas, when the damper 204 isfixed inside the image carrier drum 202 by using the adhesive, it can befixed very firmly.

The image forming apparatus in FIG. 15 has the cleaning blade 230 thatis in press contact with the surface of the image carrier drum 202 toclean the surface thereof after transferring of the toner image. It ispossible to eliminate foreign matters like paper dust etc. that arecaught between the cleaning blade 230 and the surface of the imagecarrier drum 202 by rotating the image carrier drum in the reversedirection by only a small angle when the image carrier drum is stopped.A mode for a reverse direction of rotation is set. In this mode, theimage carrier drum 202 is rotated in a reverse direction to a rotatingdirection i.e. a forward direction of the image carrier drum 202 duringformation of the toner image on the drum. However, when the mode is set,the noise that originates from the vibrations of the cleaning blade 230may be generated not only during the rotation of the drum in the forwarddirection but also during the rotation of the drum in the reversedirection. In the conventional image forming apparatus, noise tends tobe generated particularly just before the image carrier drum 202 stopsits rotation, and when the image carrier drum 202 performs operations offorward rotation, stop, reverse rotation, and stop, a loud noise isgenerated twice consecutively. However, by providing the damper 204having the structure, inside the image carrier drum 202, it is possibleto prevent generation of loud noise even during reverse rotation of theimage carrier drum 202.

Following is the explanation of the image carrier drum 202 in which thedamper 204 is fitted. As a photosensitive layer of the image carrierdrum used in electrophotography, those as follows are known. That is,the photosensitive layer includes a photosensitive layer using aninorganic semiconductor material such as selenium and amorphous silicon,a photosensitive layer using an organic semiconductor material, and aphotosensitive layer using a combination of the two. In recent years,the organic photosensitive layer has been used widely due to its lowcost, a high degree of flexibility in photoreceptor designing, andnon-polluting nature. The damper mentioned above can be fitted in theimage carrier drum having either of the photosensitive layers.

As the organic photosensitive layer used in electrophotography, those asfollows are known. That is, the organic photosensitive layer includes aphotosensitive layer of photoconductive resins represented by polyvinylcarbazole (PVK), a charge transfer complex type photosensitive layerrepresented by PVK-TNF (2,4,7-trinitrofluorenone), a pigment dispersingtype photosensitive layer represented by phthalocyanine binder, and afunction separated type photosensitive layer used as a combination ofcharge generating material with charge carrying material. Especially,the function separated type photosensitive layer has been focused on.The mechanism of forming the electrostatic latent image in the functionseparated type photosensitive layer is as follows. That is, when lightis irradiated after charging of the photosensitive layer, the lightpasses through a transparent charge carrying layer and is then absorbedby the charge generating material in the charge generating layer. Thecharge generating material that has absorbed the light generates chargecarrier, and the charge carrier is injected in the charge carrying layerto move in the charge carrying layer according to an electric fieldcreated by charging. Then, an electrostatic latent image is formed dueto neutralization of charges on the surface of the photosensitive layer.In the function separated type photosensitive layer, it is known anduseful to use a combination of the charge carrying material that absorbslight mainly in the ultraviolet region with the charge generatingmaterial that absorbs light mainly in the visible region.

However, the organic photosensitive layer has poor mechanical andchemical durability, which is a known shortcoming. Most of the chargecarrying materials is developed as low molecular compounds. However,since the low molecular compounds do not have a capacity to form amembrane independently, the compounds are used after being dispersed inand mixed with inactive high molecules. Generally, the charge carryinglayer, formed of the low molecular charge carrying material and inactivehigh molecules, is soft and has poor mechanical durability. In theelectrophotography process, mechanical load exerted by various partscoming in contact (developing, transfer paper, cleaning brush, andcleaning blade etc.) tends to break the layer easily due to repetitiveuse of the layer.

Therefore, the protective layer can be provided on the photoreceivinglayer as a top layer made of these materials to protect thephotosensitive layer and to improve the durability thereof. As explainedabove, adding of charge carrying materials to the protective layer isalso effective, and an antioxidant can also be added if necessary.

Moreover, an intermediate layer can be provided between thephotosensitive layer and the protective layer. Normally, a binder resinis used as a main component in the intermediate layer. Polyamide,alcohol-soluble nylon, water-soluble polyvinyl butyral, polyvinylbuteral, polyvinyl alcohol etc. are examples of the binder resin. Theintermediate layer is formed by the normal coating method. Theappropriate thickness of the intermediate layer is in a range ofapproximately 0.05 μm to 2 μm.

When the image carrier drum has the protective layer on its surface, thebreaking of the photosensitive layer is suppressed. Due to this, thecleaning blade can be pressed against the image carrier drum with evenstronger force. Therefore, it is possible to clean wax etc. in the tonerthat gets deposited on the image carrier drum when the toner having alow melting point is used. Moreover, the variation in the frictioncoefficient of the surface of the image carrier drum is reduced. Thatis, it is possible to have better cleaning and better noise prevention.

When filler is included in the protective layer, the breaking of thephotosensitive layer can be suppressed reliably thereby furtherimproving the effect of the protective layer.

When the charge carrying material is included in the photoelectriclayer, the breaking of the photosensitive layer can be suppressedreliably thereby further improving the effect of the protective layer.

In the image forming apparatus in FIG. 15, the image forming module 218is structured by integrally assembling the image carrier drum 202 and aplurality of image forming units used for forming the toner image on thedrum 202. However, the image forming module 218 can be structured byintegrally assembling at least the drum 202 and the cleaning blade 230that cleans the surface of the drum 202 after transferring of the tonerimage. In such a case, values of resilience and Young's modulus etc.vary due to temperature and humidity of an area around the cleaningblade 230. When the temperature and humidity increase, the cleaningblade tends to vibrate easily and the image carrier drum tends togenerate noise easily.

Therefore, it is useful to provide an environmental control unit tomaintain at least either one of the temperature and the pressure of theimage forming module at a predetermined value or below. Concretely, asensor 203 that detects either of temperature and humidity or both isprovided in the image forming module 218 as shown in FIG. 15. When thesensor 203 detects that either of temperature and pressure or bothinside the image forming module 218 is a predetermined value or more, afan (not shown) provided in the casing of the image forming apparatusstarts. The fan blows air inside the image forming module 218 in thedirection indicated by arrows E and cools down the cleaning blade 203.This reduces the generation of noise more effectively.

In the image forming apparatus shown in FIG. 15, the charging unit isformed with the charging roller 220 that is disposed close to the imagecarrier drum 202. The image carrier drum 202 with the damper insertedinto it, can also be used in an image forming apparatus that uses anyother type of charging units as shown in FIG. 18 to FIG. 20. Each of thecharging units shown in FIG. 18 to FIG. 20 is a contact type chargingunit that is in contact with the surface of the image carrier drum 202formed with a photoreceptor drum that rotates in a direction of an arrowto charge the image carrier drum 202. Each of the charging units isformed with a charging roller 220A, a brush roller 220B, or a magneticbrush unit 220C.

The charging roller 220A shown in FIG. 18 is formed with a core metal237 a and a conductive rubber layer 237 b fixed on its outer peripheralsurface. Two ends of the core metal 237 a are supported by bearings (notshown) such that the core metal can rotate freely. The charging roller220A is pressed against the image carrier drum 202 by a pressurizingunit (not shown) with prescribed pressure and rotates following therotation of the image carrier drum 202. Concretely, the rubber layer 237b having medium resistance of about 1×10⁵ ohm-cm covers the core metal237 a having a diameter of 9 millimeters. A diameter of the chargingroller 220A is 16 millimeters. The core metal 237 a is connected to apower source 250, which applies a prescribed bias to the charging roller220A. Due to application of the bias, the outer surface of the imagecarrier drum 202 is charged uniformly to a prescribed polarity andelectric potential. The damper is fitted inside the image carrier drum202. Due to the effect of the damper, the generation of noise in theimage carrier drum is reduced even when the charging voltage in which acvoltage is superimposed on dc voltage is applied to the charging roller220A.

In an example shown in FIG. 19, a brush 247 b of the brush roller 220Bis in contact with the surface of the image carrier drum 202 with aprescribed pressure so as to have a prescribed nip. The brush is made ofany of carbon, copper sulfide, metal, and metallic oxides, and issubjected to conductivity processing. The brush is wound or stuck arounda metal or any other core metal subjected to conductivity processing toform the charging roller (brush roller) 220B.

More specifically, a tape in which a conductive rayon fiber REC-B madeby UNITICA CO., LTD. is used as a pile fabric, is wound spirally as thebrush 247 b around the core metal 247 a with a diameter of 6 millimetersto form the brush roller 220B having an outer diameter of 14 millimetersand a length of 250 millimeters along the axial direction. Note that thecore metal 247 a also acts as an electrode. The brush has a density of300 deniers/50 filaments and 155 threads per one square millimeter. Thebrush 202B is inserted into a pipe having a diameter of 12 millimetersby rotating in one direction and fitted in such a way that the brush andthe pipe are concentric. Hair of the brush can be bent on one side byleaving the brush in a high temperature and high humidity atmosphere.The resistance value of the brush roller 220B is 1×10⁵ ohms for anapplied voltage of 100 volts.

This resistance value is calculated from the current that passes whenthe brush roller 220B is brought into contact with the metal drum havinga diameter of 30 millimeters with a nip width of 3 millimeters and avoltage of 100 volts is applied to the core metal 247 a. The resistancevalue of the brush roller has to be 10⁴ ohms or more so that even if adefective part of the low withstand voltage such as a pinhole isproduced on the image carrier drum as a charged body, there is no poorcharging of the charging nip due to an excessive leakage current in thispart and defective image forming is prohibited. The resistance value ofthe brush roller has to be 10⁷ ohms or less to inject sufficient chargeon the surface of the image carrier drum.

The material for the brush includes REC-C, REC-M1, REC-M10 in additionto REC-B made by UNITICA CO., LTD, SA-7 made by TORAY CO., LTD,Thunderon made by NIHON SANMO CO., LTD, Belltron made by KANEBO CO.,LTD, Clacarbo made by KURARAY CO., LTD, a material obtained bydispersing carbon into rayon, and Lobal made by MITSUBISHI RAYON CO.,LTD. It is preferable that a line of brush is in a range of 3 deniers to10 deniers, and the brush is in a range of 10 filaments to 100 filamentsper bunch, and has 80 threads to 600 threads per millimeter. Thepreferable length of brush hair is in a range of 1 millimeter to 10millimeters.

The brush roller 220B in the example is driven to rotate at a prescribedcircumferential velocity (speed of the surface) in a reverse direction(counter direction) to the rotating direction of the image carrier drum202. The brush roller 220B is in contact with the surface of the imagecarrier drum 202 with a different speed as that of the drum. A powersupply 250 applies a prescribed charging voltage to the brush roller220B, and the rotating image carrier drum is charged uniformly to aprescribed polarity and electric potential by the brush roller incontact with the drum. In the example, the brush roller 220B carries outthe contact charging to the image carrier drum dominantly by directinjection charging, and the surface of the image carrier drum is chargedto almost the same electric potential as the applied charging voltage tothe brush roller. The damper is fitted inside the image carrier drum 202in FIG. 19 as well. Due to the effect of the damper, the generation ofnoise in the image carrier drum 202 is reduced even if the chargingvoltage in which ac voltage is superimposed on dc voltage is applied tothe brush roller 220B.

In an example in FIG. 20, a charging unit that uses a magnetic brush isprovided adjacent to the image carrier drum 202. A magnetic brush MB isarranged such that it is in contact with the peripheral surface of theimage carrier drum 202 with a prescribed nip.

A magnetic brush unit 220C in the example includes a non-magnetic sleeve257 a that supports the magnetic brush MB and a magnetic roller (notshown) incorporated in the non-magnetic sleeve 257 a. Various types offerrite particles like Zn—Cu ferrite can be used as particles for themagnetic brush. More specifically, the magnetic brush is formed asfollows. The Zn—Cu ferrite particles of an average particle size: 25 μmare mixed with Zn—Cu ferrite particles of an average particle size: 10μm in the ratio of weights 1: 0.05 respectively. The ferrite particlesof an average particle size 25 μm which have peaks in respectivepositions of the average particle size, are coated with a resin layer ofmedium resistance to give magnetic particles. The sleeve 257 a is coatedwith the coated magnetic particles by a thickness of 1 millimeter toform the magnetic brush.

The magnetic particles are carried on the sleeve 257 a by magnetic forceof the magnetic roller that is incorporated in the sleeve 257 a. Such amagnetic brush MB forms a charging nip having a width of about 5millimeters (width of the direction of rotation) between the magneticbrush MB and the image carrier drum 202, and enables to adjust the gapbetween the sleeve 257 a that holds the magnetic particles and the imagecarrier drum 202 to about 500 μm.

Moreover, it is preferable that the non-magnetic sleeve 257 a is rotatedso that the surface of the sleeve 257 a moves in the direction oppositeto the direction of moving of the surface of the image carrier drum at aspeed double with respect to the peripheral velocity of the imagecarrier drum. It is also preferable that the magnetic brush is made toscrape the surface of the image carrier drum, and that the image carrierdrum and the magnetic brush are in uniform contact with each other. Aprescribed charging voltage is applied to the sleeve 257 a by the powersource 250 and the image carrier drum is charged uniformly to aprescribed polarity and electric potential through the magnetic brushMB. The damper is fitted inside the image carrier drum 202 in FIG. 20 aswell. Due to the effect of the damper, the generation of noise in theimage carrier drum 202 is reduced even if the charging voltage in whichac voltage is superimposed on dc voltage is applied to the drum 202 byusing a contact type charging unit like the magnetic brush unit 220C inthe example.

The present invention can be applied to a color image forming apparatusin which plurality of image carrier drums, i.e. photoreceptor drums arelined up. Moreover, the present invention is also applicable to anytypes of image forming apparatuses like a printer, a facsimile, acopying machine, and a multifunction machine of these apparatuses.

Thus, the example of the image carrier drum that is formed with aphotoreceptor drum and is provided with the damper inside the imagecarrier drum is explained here. However, even in a case of the imagecarrier drum formed with an intermediate transfer drum to which thetoner image is transferred from the photoreceptor, the generation ofnoise from the intermediate transfer drum can be reduced effectively byproviding the damper inside the intermediate transfer drum. Moreover,the generation of noise can be reduced by providing the damper insidethe roller that supports the photoreceptor in the form of an endlessbelt and the intermediate transfer belt.

Thus, according to the second embodiment, the generation of noise can beeffectively reduced even if the toner having a low melting point isused.

A third embodiment of this invention will be explained below.

FIG. 21 is a cross section of an image forming unit of an image formingapparatus provided with an image carrier drum according to the thirdembodiment. An image carrier drum 202 in the figure is a photoreceptordrum which includes a photosensitive layer provided on an outerperipheral surface of a circular cylindrical tube made of a conductivemetal like aluminum. The image carrier drum 202 is supported by a shaft301 that extends through inside the image carrier drum 202 as explainedlater. Both ends of the shaft 301 along its length are supported by acase 219 of an image forming module 218. The image carrier drum 202supported by the shaft 301 is rotated by a drive motor (not shown) in aclockwise direction as shown in FIG. 21. During rotation of the imagecarrier drum 202, a charging unit formed with a charging roller 220rotatably supported by the case 219 rotates while being in contact withthe outer peripheral surface of the image carrier drum 202. The surfaceof the image carrier drum 202 is charged to a prescribed polarity byapplying a charging voltage to the charging roller 220.

A modulated laser beam L emitted from an exposing unit (not shown) isirradiated on the surface of the image carrier drum 202 after beingcharged to form an electrostatic latent image on the image carrier drum.The exposing unit is provided separately apart from the image formingmodule 218. This electrostatic latent image is visualized as a tonerimage by a developing unit 222. The toner image is carried on a transferbelt 208 and is transferred to a transfer paper P that travels in adirection of an arrow A by an action of a transfer brush 209. The tonerimage having been transferred to the transfer paper P is fixed on thetransfer paper by a fixing unit (not shown). A residual toner on theimage carrier drum after the transferring of the toner image iseliminated by combined action of a charging brush 229 and a cleaningblade 230 of a cleaning unit 227.

The developing unit 222 includes a developing case 223 that is formedwith a part of the case 219 of the image forming module 218 and adeveloping roller 224 that is rotatably supported by the developing case223. The developing case 223 contains developer D. The developer D iscarried on the rotating developing roller 224 and transferred, and theelectrostatic latent image is visualized by the transferred developer.In this case, a two-component developer, which includes toner andcarrier, is used as the developer. When a decrease in toner density ofthe developer is detected, the toner is replenished from a tonercontainer 233. The cleaning unit 227 includes a cleaning case 228 thatis also formed with a part of the case 219 of the image forming module218. The cleaning brush 229 and the cleaning blade 230 are supported bythe cleaning case 228. The toner recovered from the image carrier drum202 is returned to the toner container 233 through a toner carrier tube231 connected to the case 219.

Thus, in the image forming apparatus shown in FIG. 21, the image carrierdrum 202 and the image forming units provided around the drum 202 suchas the charging roller 220, the developing roller 224, the cleaningbrush 229, the cleaning blade 230 are integrally assembled to the case219 and the image forming module 218 is formed thereby. The imageforming module 218 is detachable from a casing (not shown) of the imageforming apparatus and can be replaced by a new image forming module whenthe module reaches end of its life.

FIG. 22 is a longitudinal cross section of the image carrier drum 202.Ordinary flanges 303 and 303A are fitted to ends of the image carrierdrum 202 in its axial direction of this figure. The shaft 301 passesthrough the flanges 303 and 303A and extends through inside the imagecarrier drum 202. The image carrier drum 202 is supported by the shaft301 through the flanges 303 and 303A. The shaft 301 is disposedconcentrically with the image carrier drum 202 and extends through thecenter of the image carrier drum 202.

A gear 305 is integrated on the outer periphery of the flange 303. Acounter gear (not shown) engages with the gear 305. A drive motor (notshown) rotates the flange 303 by transmitting the rotations through thegear 305 and the counter gear. The rotations of the flange 303 aretransmitted to the image carrier drum 202, and the image carrier drum202 rotates around the axis of its center. As shown in FIG. 23, a notch306 is formed at an edge of the image carrier drum 202. A protrusion 307provided on the flange 303 is engaged in the notch 306 therebytransmitting the rotation of the flange 303 to the image carrier drum202. The flanges 303 and 303A may be press fitted into the ends of theimage carrier drum 202, or may be fixed to the image carrier drum 202with an adhesive. The flanges 303 and 303A may also be engaged with theimage carrier drum 202 by clearance fit. When the flanges 303 and 303Aare engaged by the clearance fit, it is necessary to hold the flanges byusing thrust stoppers (not shown), which are provided to stop theflanges 303 and 303A from moving in the axial direction of the imagecarrier drum 202 and coming off. A sidewall of the case 219 shown inFIG. 21 can be used as the thrust stopper.

The shaft 301 passing through the flanges 303 and 303A may be fixed tothe flanges by press fit. The shaft 301 may also be engaged with theflanges 303 and 303A such that the flanges can rotate freely around theshaft 301. In the former case, the shaft 301 rotates together with theflange 303, flange 303A, and the image carrier drum 202 whereas in thelatter case the shaft 301 does not rotate. In either of the cases, theshaft 301 is supported by the case 219 as shown in FIG. 21.

The charging roller 220 and the cleaning blade 230 are in contact withthe outer peripheral surface of the image carrier drum 202 as shown inFIG. 21. When a charging voltage having ac voltage superimposed on dcvoltage is applied to the charging roller 220, the charging roller 220vibrates due to the application of the ac voltage. Further, the cleaningblade 230 vibrates due to stick-slip during rotation of the imagecarrier drum 202. These vibrations are transmitted to the drum 202, andthe drum 202 vibrates. If these vibrations become strong, then noise isproduced.

Therefore, a damper 204 (204G) is disposed inside the image carrier drum202 of this embodiment as shown in FIG. 21 and FIG. 22. The damper 204Gshown in the figures is in the form of a cup having almost U-shapedlongitudinal cross sectional form. The shaft 301 passes through a hole310 that is made in the bottom wall of the damper 204G. The damper 204Gcan be made of an appropriate material like an elastic material, a rigidmaterial such as rubber, resin, and metal, or a combination of thesematerials. The damper 204 having an outer diameter slightly smaller thanan inner diameter of the image carrier drum 202 is used, and such adamper 204 may be fixed to the inner wall surface of the image carrierdrum 202 with an adhesive. Alternatively, the damper 204 having an outerdiameter before being inserted into the drum 202 that is slightly biggerthan an inner diameter of the drum 202 is used. When such a damper 204is inserted inside the drum 202, the damper 204 may be elasticallydeformed in the direction in which the diameter is contracted. Thus, thedamper 204 may be pressed against the inner wall surface of the drum 202and fixed to the drum 202.

Thus, a cylinder unit 312 is integrally formed with the cylinder (theimage carrier drum 202 in the example), a shaft that supports thecylinder, and a damper that is disposed inside the cylinder. The shaft301 passes through the cylinder and further extends. In the exampleshown in FIG. 22, the pair of flanges 303 and 303A is also included inthe cylinder unit 312. The damper 204 is provided inside the imagecarrier drum 202, which makes it possible to reduce the vibrations inthe image carrier drum 202 and effectively suppress the generation ofnoise.

The image carrier drum 202 goes on deteriorating with time and when itreaches end of its life, the image forming module 218 shown in FIG. 21is removed from the body of the apparatus and replaced by a new imageforming module. The image forming module 218 removed from the body ofthe apparatus is recycled. That is, the cylinder unit 212 is removedfrom the case 219 of the image forming module 218 and disassembled intocomponents. The components that can be reused in the existing conditionare reused as they are, and the other components are subjected toprescribed recycling processing and are provided for reuse.

To facilitate the recycling of the cylinder unit 212, i.e. to be able toremove the damper 204 from the image carrier drum 202, the cylinder unit212 is structured as follows. As shown in FIG. 22, a protrusion 313having a diameter bigger than that of the shaft 301 is integrated withthe shaft 301. A portion 311 of the damper 204 facing the protrusion313, is positioned such that the portion 311 is in contact with theprotrusion 313. The flange 303A on the other side is pulled out from theshaft 301 and removed. In the case where the flange 303A is fixed to theimage carrier drum 303 with an adhesive, the flange 303A is applied withforce to break the adhesive and is separated from the shaft 301 and theimage carrier drum 202.

Then, the shaft 301 is moved in the direction shown by an arrow B inFIG. 22, i.e. in the axial direction of the image carrier drum 202. Whenthe shaft 301 is moved, the protrusion 313 that is fixed to the shaft301 comes in contact with a portion 311 of the damper 204 (hereinafter“contacting portion”) and pushes the area in the direction of the arrowB. Due to this, the damper 204 moves in the axial direction of the imagecarrier drum, i.e. the direction of the arrow B together with the shaft301. In the case where the damper 204 is fixed to the inner wall surfaceof the image carrier drum 202 with an adhesive, the damper 204 is pushedin the direction of the arrow B to break the adhesive, and is moved inthe direction of the arrow B.

While moving the damper 204, the shaft 301 slides with respect to theflange 303. As shown in FIG. 24, when the shaft 301 is moved further inthe direction of the arrow B, the damper 204 moving together with theshaft 301 pushes the flange 303, and therefore the flange 303 is removedfrom the image carrier drum 202. In this case also, when the flange 303is fixed to the image carrier drum 202 with an adhesive, by applying anexternal force to the flange, the adhesive is broken. Moreover, when theshaft 301 is moved further in the direction of the arrow B, the damper204 is eventually removed from the image carrier drum 202. In the casewhere the flange 303 is fixed to the image carrier drum 202 by clearancefit, the flange 303 can be removed from the image carrier drum 202before the damper 204 comes in contact with the flange 303. Thus, justby pulling out the shaft 301, the damper 204 and the flange 303 can beremoved from the image carrier drum 202 thereby enabling disassemble ofthe cylinder unit with ease and at a low cost without using any specialtools.

As explained above, the cylinder, the shaft 301, and the damper 204 areassembled such that when the shaft 301 is pulled out from the cylinderas the image carrier drum 202, the damper 204 moves in the axialdirection of the cylinder together with the shaft 301 and is removedfrom the cylinder. Moreover, in the cylinder unit 312, the protrusion313 protruding in the radial direction of the shaft 301 is provided onthe shaft 301. The damper 204 has the contacting portion 311 that comesin contact with the protrusion 313 when the shaft 301 is pulled out fromthe cylinder. The protrusion 313 is brought into contact with thecontacting portion 311 and the damper 204 is moved together with theshaft 301 thereby simplifying the structure of the cylinder unit 312.

Furthermore, the contacting portion 311 of the damper 204 is positionedat the front end in the movement direction of the damper 204. Therefore,if the damper 204 is made of an elastic material, the damper 204 isdeformed by reducing its diameter when the shaft 301 and the damper 204move in the direction of the arrow B, which allows the damper 204 to beeasily moved inside the image carrier drum. Assume that the protrusion313 fixed to the shaft 301 is structured such that the protrusion 313pushes the rear end of the damper 204 made of an elastic material in themovement direction of the damper 204. The frictional force that actsbetween the damper 204 and the inner wall surface of the image carrierdrum is exerted on the damper 204. Due to this frictional force, thedamper 204 expands in the radial direction and cannot be moved smoothly.However, since the contacting portion 311 is at the front end of thedamper 204 in the direction of its movement, there is no hindrance tothe movement of the damper.

The shaft 301, the damper 204, the flange 303, and the flange 303A whichare disassembled in the above manner, can be reused as they are only bycleaning these components. Moreover, since the damper 204 in thecylinder unit 312 is disposed in the space surrounded by the imagecarrier drum 202, the flange 303, and the flange 303A, the damper 204 isnot contaminated by either of dust and toner during the use of thecylinder unit 312. Therefore, the damper 204 can also be reused withoutcleaning after it is separated from the image carrier drum.

The assembling of the cylinder unit 312 is also facilitated. Forexample, the damper 204 is disposed on the left side of the imagecarrier drum 202 in FIG. 22 and the shaft 301 on which the flanges 303and 303A are not fixed is inserted inside the image carrier drum 202from the left end of the drum 202. While inserting the shaft 301, theshaft 301 is passed through the hole 310 of the damper 204, and thecontacting portion 311 of the damper 204 is pushed by the protrusion 313provided on the shaft 301. While pressurizing the damper 204 in thedirection of the arrow B in FIG. 22, the shaft 301 together with thedamper 204 is inserted into the image carrier drum 202. Then, theflanges 303 and 303A are fitted to the ends of the shaft 301 and alsofitted on the ends of the image carrier drum 202 thereby fitting thedamper 204 inside the image carrier drum 202.

Further, as shown in FIG. 25 and FIG. 27, the damper 204 can also beintegrally coupled to the shaft 301. FIG. 25 illustrates an example offixing a hollow circular cylindrical shaped damper 204 to the shaft 301,and FIG. 26 illustrates an example of using a damper 204 in which aplurality of circular discs 204A are integrated with a base 204B andfixing the base 204B to the shaft 301. FIG. 27 illustrates an example offixing a plurality of circular shaped discs 204C to the shaft 301 toform a damper 204.

For disassembling the components of cylinder units 312 shown in FIG. 25to FIG. 27, when the shaft 301 is moved in the direction of the arrow Bafter the flange 303A is separated from the shaft 301 in the same manneras explained above, the damper 204 that is integrally coupled to theshaft 301 also moves with the shaft 301, which allows the flange 303 andthe damper 204 to be separated from the image carrier drum 202. The restof the structures shown in FIG. 25 to FIG. 27 are practically similar tothose shown in FIG. 21 to FIG. 24.

The effect similar to that of the cylinder units 312 shown in FIG. 25 toFIG. 27 can be achieved also by fixing a solid cylindrical damper to theshaft 301. However, when the solid damper is moved inside the imagecarrier drum 202, the solid damper undergoes a considerable amount offrictional force from the inner wall surface of the image carrier drum202, and therefore smooth movement of the damper becomes difficult. Whenthe dampers 204, shown in FIG. 25 to FIG. 27, are made of an elasticmaterial in particular, the dampers 204 undergo elastic deformationeasily when they are moved inside the image carrier drum 202. Therefore,the frictional force exerted by the inner wall surface of the imagecarrier drum 202 decreases and the dampers 204 can be moved easily.

Moreover, in the example shown in FIG. 22, when the diameter of theimage carrier drum 202 is small, the diameters of the damper 204 and theprotrusion 313 also become smaller, and a contact area between theprotrusion 313 and contacting portion 311 of the damper 204 becomessmaller. Therefore, when the shaft 301 is moved in the direction of thearrow B, the pressure per unit area of the contact surface between theprotrusion 313 and the contacting portion 311 increases. Therefore,especially in the case of the damper 204 made of an elastic material,the portion of the damper 204 pushed by the protrusion 313 undergoesconsiderable elastic deformation. Due to the elastic deformation, theforce is not conveyed properly from the protrusion 313 to the damper204, and therefore the damper 204 may not be moved smoothly. To avoidthis, the damper 204 is integrally coupled to the shaft 301 to make itmove easily together with the shaft 301 when the shaft 301 is pulled outfrom the cylinder as shown in the examples in FIG. 25 to FIG. 27. Thus,the damper 204 can reliably be moved and can be removed from the imagecarrier drum 202 easily.

The cylinder unit 312 has a pair of flanges 303 and 303A fitted to theends of the cylinder formed with the image carrier drum 202 in the axialdirection. The cylinder is supported by the shaft 301 through theseflanges 303 and 303A. The shape of the damper is set so that the damper204 moves in the axial direction of the cylinder to come in contact withthe flange 303 and pushes the flange 303, and then the flange 303 isremoved from the cylinder. Therefore, as explained above, the flange 303can be separated from the cylinder just by pulling out the shaft 301.Thus, the workability can be enhanced.

The damper 204 can be formed by an appropriate material as explainedabove. As shown in FIG. 28, in a case of pulling out the shaft 301 fromthe image carrier drum 202, if a portion 314 of the damper coming incontact with the flange 303 is made of a rigid material, by bringing theportion 314 of the damper into contact with the flange 303 andpressurizing the flange 303, the force can be appropriately conveyed tothe flange 303. Thus, the flange can be separated easily from the imagecarrier drum 202. The portion 314 of the damper can be made of ABS resinor metal having a Young's modulus of about 2 to 3 GPa.

When the portion 314 of the damper is made of the rigid material, if thespeed at which the shaft 301 is pulled out is high, the portion 314 ofthe damper impacts against the flange 303 and may damage the flange 303.In a case of such concern, the portion 314 of the damper coming incontact with the flanges 303 may be made of an elastic material. Forexample, the portion 314 of the damper is made of rubber having aYoung's modulus of about 0.5 to 1.5 MPa. Thus, even when the portion 314impacts against the flange 303, the damage of the flange 303 can beprevented and reused without any trouble.

As shown in FIG. 29, the flange 303 can be structured to have a firstcylinder member 315 that fits to the ends of the cylinder formed withthe image carrier drum 202 in the axial direction and a second cylindermember 316 that fits into the first cylinder member 315. In thisexample, a gear 305 is formed on the first cylinder member 315. FIG. 30is an exploded perspective view of the first cylinder member 315 and thesecond cylinder member 316. To fit the flange 303 to the image carrierdrum 202, as shown in FIG. 31, the first cylinder member 315 is fittedinto the end of the image carrier drum 202 and then the second cylindermember 316 is fitted into the first cylinder member 315. In this case,assume that an outer diameter of the second cylinder member 316 beforeit is fitted into the first cylinder member 315 is D1, a thickness of apart of the first cylinder member 315 that is inserted in the imagecarrier drum 202 is T, and an inner diameter of the image carrier drum202 is D2. Each diameter and thickness are set so as to be D1+2T>D2.Thus, when the second cylinder member 316 is fitted in the firstcylinder member 315 as shown in FIG. 29, the part of the first cylindermember 315 that is inserted into the image carrier drum 202 is in presscontact with the inner wall surface of the image carrier drum 202 andthe whole of the flange 303 is fixed to the image carrier drum 202.

Thus, the second cylinder member 316 is fitted in the first cylindermember 315, the first cylinder member 315 is made to be in pressedcontact with the inner wall surface of the cylinder of the drum 202 andthe flange is fixed on the cylinder. A plurality of slits 340 is formedin the first cylinder member 315 as shown in FIG. 30, and therefore thefirst cylinder member 315 can be pressed easily against the inner wallsurface of the image carrier drum 202 by the second cylinder member 316.The shaft 301 is passed through a hole 342 in the second cylinder member316 as shown in FIG. 29. The shaft 301 can be assembled with the imagecarrier drum 202 after fixing the flange 303 to the image carrier drum202. The shaft 301 can also be inserted into the image carrier drum 202before fixing the flange 303 to the image carrier drum 202. For theflange 303A (FIG. 22, FIG. 25), any of the flanges shown in FIG. 29 toFIG. 31 can be used.

When the flange 303 is structured in this manner, if the diameter of thefront end of the damper 204 that faces the flange 303 is made smaller asshown in FIG. 29 and the damper 204 is moved together with the flange303 in the direction of the arrow B, then it is preferable to structuresuch that a front end surface 341 of the front end comes in contact onlywith the second cylinder member 316. That is, the arrangement is madesuch that the damper 204 moves in an axial direction of the cylinder,the front end surface 341 of the damper 204 comes in contact only withthe second cylinder member 316, and pushes the second cylinder member316. With this arrangement, the second cylinder member 316 and the firstcylinder member 315 are separated apart from each other due to thesecond cylinder member 316 pushed by the damper 204. Thus, the firstcylinder member 315 and the second cylinder member 316 can be removedfrom the image carrier drum 202 without applying heavy load on them.This prevents causing of any damage to the first cylinder member 315 andthe second cylinder member 316 thereby enabling their reuse without anyprocessing after disassembling.

According to the embodiment, the damper 204 can be integrated with thecylinder including the image carrier drum 202 as an integral assembly bypress fitting the damper on the inner wall surface of the cylinder dueto elastic property of the damper 204. When the damper 204 is fixed tothe image carrier drum 202 without using any adhesive material, theshaft 301 can be pulled out from the image carrier drum 202 easilythereby facilitating disassembling of the image carrier drum 202.

As explained above, the cylinder of the image carrier drum 202, the pairof the flanges 303 and 303A, and the shaft 301 are assembled together torotate as an integrated assembly by press fitting the flanges 303 and303A to the shaft 301 so as to be fixed to each other. Therefore, theflanges 303 and 303A cannot rotate around the shaft 301 since they arefixed. This prevents the sliding contact between the shaft 301 and theflanges 303 and 303A thereby preventing wearing away of the three. Thus,the shaft 301 and the flanges 303 and 303A can be reused afterdisassembling without carrying out any special machining process onthem.

In the embodiment, the cylinder is the image carrier drum 202 on which atoner image is formed. In other words, although the cylinder in thisexample is a photoreceptor drum, when the cylinder is any device otherthan the image carrier drum, these structures can be employed.Concretely, the cylinder includes an image carrier drum that includesintermediate transfer body on which a toner image formed on thephotoreceptor drum is transferred, a charging roller, a developingroller, transfer paper carrier roller, and any other cylinder formed asa support for a structure.

Moreover, the image forming apparatus in FIG. 21 includes the imagecarrier drum 202, and the image forming module that is assembled byintegrating the image forming elements like the charging roller 220, thedeveloping roller 224, the cleaning brush 229, and the cleaning blade230 to form the image on the image carrier drum 202. It is a normalpractice to reduce the size and weight of this image forming module tomake it easy to handle.

Therefore, since small sized elements are used in the image formingmodule, the life of the image forming module is short. In the imageforming apparatus in FIG. 21, an arrangement is made to replenish thetoner container 233 with toner. However, when there is no arrangementfor replenishment of the toner and when the structure is made such thatthe image forming module is to be replaced after the toner in thedeveloping unit gets exhausted, the life of the image forming modulebecomes further short. The short life of the image forming moduleimplies increased number of the image forming modules that aremanufactured and are in the market. Therefore, it is important tofacilitate the disassembling of the cylinder unit 312 and improverecycling. By structuring the cylinder unit 312 as mentioned in theembodiment, the cylinder unit 312 can be easily recycled, and the demandcan be surely satisfied.

The cylinder unit can also be made discretely detachable from the mainbody of the image forming apparatus. In this case, it is a normalpractice to set the life of the image carrier drum longer than that ofthe image forming unit that forms an image on the image carrier drum andto go on replacing the image carrier drum while the image formingapparatus is being used. In such a case also, by structuring thecylinder unit 312 as mentioned in this embodiment to improve recycling,it is possible to reuse the components of the cylinder unit 312 easily.

Thus, according to the third embodiment, the recycling is facilitated bystructuring the cylinder unit such that it can be easily disassembled.

A fourth embodiment of this invention will be explained below.

FIG. 32 is a schematic diagram of an image forming section of the imageforming apparatus that uses an image carrier drum according to thefourth embodiment. An image carrier drum 202 in the figure is aphotoreceptor drum which includes a circular tube made of a conductivemetal like aluminum with a photosensitive layer provided on an outerperipheral surface. The image carrier drum 202 is rotatably supported bya case 219 of a process cartridge 218 and is rotated by a drive motor(not shown) in the clockwise direction in FIG. 32. A charging unitincluding a charging roller 220 rotatably supported by the case 219 isin contact with the image carrier drum 202 and rotates. By applying acharging voltage to the charging roller 220, a surface of the imagecarrier drum 202 is charged to a prescribed polarity.

A modulated laser beam L is irradiated on the surface of the imagecarrier drum 202 after being charged, the beam being emitted from anexposing unit (not shown) provided separately apart from the processcartridge. Thereby an electrostatic latent image is formed on the imagecarrier drum 202. This electrostatic latent image is visualized as atoner image by a developing unit 222. The toner image is carried on atransfer belt 208 and is transferred to a recording medium P such as atransfer paper that travels in a direction of an arrow A, by an actionof a transfer brush 209 as an example of the transfer unit. The tonerimage having been transferred to the recording medium P is fixed on therecording medium by the fixing unit (not shown). A residual toner on theimage carrier drum that remains after the transferring of the tonerimage is eliminated by combined action of a cleaning brush 229 and acleaning blade 230 of a cleaning unit 227.

The developing unit 222 includes a developing case 223 formed with apart of the case 219 of the process cartridge 218 and a developingroller 224 rotatably supported by the developing case 223. Thedeveloping case 223 contains developer D. The rotating developing roller224 carries and conveys the developer D. The conveyed developervisualizes the electrostatic latent image. In this case, a drytwo-component developer including toner and carrier, is used asdeveloper, and when a decrease in toner density of the developer isdetected, the toner is replenished from a toner container.

The cleaning unit 227 includes the cleaning case 228 also formed with apart of the case 219 of the process cartridge 218. The cleaning brush229 and the cleaning blade 230 are supported by the cleaning case 228.The toner recovered from the image carrier drum 202 is returned to thetoner container 233 through a toner carrier tube 231 connected to thecase 219.

FIG. 33 is a longitudinal cross section of the image carrier drum 202.Flanges 303 and 303A are fitted at each end of the image carrier drum202 in the axial direction. The flanges 303 and 303A are rotatablysupported by the case 219 (FIG. 32), and the image carrier drum 202 isthereby rotatably supported by the case 219. It is possible to omit oneof the flanges 303 and 303A. It is also possible to omit both theflanges, and both ends of the image carrier drum 202 can be rotatablysupported directly by the case 219. When it is necessary to distinguishthese flanges 303 and 303A from each other, the flange 303 is referredto as a first flange and the flange 303A is referred to as a secondflange.

A gear 305 is integrated on the outer peripheral surface of the secondflange 303A. A counter gear, which is not shown in the figure, isengaged with the gear 305. A drive motor, which is also not shown in thefigure, rotates the second flange 303A by transmitting the rotationsthrough these gears. The rotations of the flange 303A are transmitted tothe image carrier drum 202, and the drum 202 rotates around the centralaxis of the flange 303A. A notch 306 is made at an end of the imagecarrier drum 202 as shown in FIG. 23. A protrusion 307 provided on thesecond flange 303A is engaged in the notch 306 thereby preventingrelative rotation of the second flange 303A and the image carrier drum202 and transmitting the rotation of the flange 303A to the imagecarrier drum 202.

The flanges 303 and 303A may be press fitted into openings at the endsof the image carrier drum 202 or may be fixed to the image carrier drum202 with an adhesive. The flanges 303 and 303A can also be engaged withthe image carrier drum by clearance fit. When the flanges 303 and 303Aare engaged by clearance fit, it is necessary to hold the flanges byusing thrust stoppers not shown in the figure, which are provided tostop the flanges 303 and 303A from moving in the axial direction of theimage carrier drum 202 and from being removed from the drum 202. Asidewall of the case 219 shown in FIG. 32 can be used as a thruststopper.

The charging roller 202 and the cleaning blade 230 are in contact withthe outer peripheral surface of the image carrier drum 202 as shown inFIG. 32. When a charging voltage having ac voltage superimposed on dcvoltage, is applied to the charging roller 220, the charging roller 220vibrates due to the application of the ac voltage. Further, the cleaningblade 230 vibrates due to stick-slip during rotation of the imagecarrier drum 202. These vibrations are transmitted to the image carrierdrum 202, due to which the drum 202 vibrates. When these vibrationsbecome strong, noise is produced.

Therefore, a damper 404 is disposed inside the image carrier drum 202 ofthis example as shown in FIG. 32 and FIG. 33. The damper 404 includes acylinder 417 having an outer peripheral surface 414 that is fixed to theinner peripheral surface of the image carrier drum 202, and a sidewall410. The damper 404 is in the form of a cup having almost U-shapedlongitudinal cross sectional form. An end of the damper 404 opposite tothe sidewall 410 is kept open as an open end.

The damper 404 can be made of an appropriate material such as an elasticmaterial, a rigid material such as rubber, resin, and metal, or acombination of these materials.

The damper 404 having an outer diameter slightly smaller than an innerdiameter of the image carrier drum 202 may be used and fixed to theinner surface of the image carrier drum 202 with an adhesive. The damper404 having an outer diameter before being inserted into the drum 202that is slightly bigger than an inner diameter of the drum 202 may beused and inserted into the image carrier drum 202. When the damper 404is inserted into the drum 202, the damper 404 undergoes elasticdeformation in the direction of contraction of the diameter. Thus, thedamper 404 can be fixed inside the image carrier drum 202 by making apressed contact with an inner surface of the drum 202.

Thus, the damper 404 mounted inside the image carrier drum 202 is heldinside the image carrier drum 202 due to the pressed contact with theinner surface of the image carrier drum 202. The pressed contact isattributed to the elasticity of the material of the damper.Alternatively, the damper 404 is fixed on the inner wall surface of theimage carrier drum 202 with an adhesive. The damper 404 may also befixed on the inner wall surface of the image carrier drum 202 using bothelasticity and the adhesive.

The damper 404, which is provided inside the image carrier drum 202,reduces vibrations of the image carrier drum 202 and effectivelysuppresses the generation of noise.

Moreover, in the image forming apparatus of this example, an integrateddrum unit 434 is structured by assembling the image carrier drum 202with the damper 404 that is mounted inside the drum and the pair offlanges 303 and 303A. It is also possible to structure the integrateddrum unit 434 without the flanges 303 and 303A. The drum unit 434includes at least the image carrier drum 202 and the damper 404.

Further, in the image forming apparatus of this example, the processcartridge 218 is structured by assembling the drum unit 434 integratedwith the image forming units such as the charging roller 220, thedeveloping unit 222, the cleaning unit 227, which are disposed aroundthe drum unit 434. Suitable image forming units can be selected forforming the process cartridge 218. In short, the process cartridgeincludes a drum unit and at least an image forming unit that forms atoner image on an image carrier drum of the drum unit. The processcartridge is detachable from the main body of the image formingapparatus. The image forming apparatus of this example includes eitherof the process cartridge 218 and the drum unit 434.

The image carrier drum 202 goes on deteriorating with time and when itreaches end of its life, the process cartridge 218 shown in FIG. 32 isremoved from the main body of the image forming apparatus and replacedby a new process cartridge. The process cartridge 218 removed from themain body of the image forming apparatus is recycled. In recyclingprocess, the image carrier drum 202 is removed from the case 219 of theprocess cartridge 219. The image carrier drum 202 and the componentsthat are assembled together with the drum are disassembled. Thecomponents that can be reused in the existing condition are reused asthey are, and the rest of the components are subjected to predeterminedmachining or treatment process, and are provided for reuse.

To facilitate the recycling of the image carrier drum 202, the damper404, and the flanges 303 and 303A that are assembled with the drum, thefollowing method is employed to easily assemble and disassemble thesecomponents.

FIG. 34 and FIG. 35 are cross sections of how a damper 404 is fixed toan image carrier drum 202. In the example shown here, an image carrierdrum 202 without flanges 303 and 303A fixed on it is prepared. Asidewall 410 of the damper 404 is made to face an opening 411 on one endin the axial direction of the image carrier drum 202 as shown in FIG.34. In the examples shown in FIG. 34 and FIG. 35, the damper 404 is madeof an elastic material like rubber. An outer diameter of the damper 404before being inserted into the image carrier drum 202 is set to beslightly bigger than an inner diameter of the image carrier drum 202.

In the state as shown in FIG. 34, a force imparting member 413 in theform of a rod is inserted into a cylinder 417 of the damper 404 in thedirection of an arrow B from the opening end of the damper 404. Afront-end 413A of the force imparting member 413 is brought into contactwith the sidewall 410 of the damper 404 and the force imparting member413 is pushed further in the direction of the arrow B along the axialdirection of the image carrier drum 202. Thus, the damper 404 is thrustinside the image carrier drum 202 as shown in FIG. 35 and moved up tothe position shown in FIG. 33. Then, the force imparting member 413 ispulled in a direction opposite to that of the arrow B and pulled outfrom the image carrier drum. Thus, the damper 404 having the outerdiameter before being inserted into the drum 202 that is slightly biggerthan an inner diameter of the image carrier drum 202, can be insertedand mounted inside the image carrier drum 202 with ease.

The damper 404 mounted inside the image carrier drum 202 is fixed to theimage carrier drum 202 by pressing an outer peripheral surface 414 ofthe cylinder 417 against the inner peripheral surface of the drum 202 bythe elasticity. The first flange 303 and the second flange 303A arefixed on the opening 411 and an opening 412 on both ends in the axialdirection of the drum 202 respectively as shown in FIG. 33. The imagecarrier drum 202 thus formed is assembled with the case 219 shown inFIG. 32 and used.

The outer peripheral surface 414 of the damper 404 can also be fixed tothe inner peripheral surface of the image carrier drum 202 with anadhesive. When the damper 404 is made of a rigid material, the damper404 can be inserted into the image carrier drum 202 and fixed to theinner peripheral surface of the image carrier drum 202 in the samemanner as explained above.

When the image carrier drum 202 and the damper 404 are to bedisassembled, first of all the first flange 303 is removed from theimage carrier drum 202 as shown in FIG. 33. When the flange 303 is fixedto the image carrier drum 202 with an adhesive, a force is applied tothe flange 303 to break the adhesive, and the flange 303 is separatedapart from the image carrier drum 202. Then, as shown in FIG. 36, theforce imparting member 413 is inserted into the image carrier drum 202from the opening 411, and further inserted into the cylinder 417 fromthe open end of the damper 404, and the front end 413A of the forceimparting member 413 is brought into contact with the sidewall 410. Theforce imparting member 413 is further pushed in the direction of anarrow B. Due to this, the damper 404 moves in the axial direction of theimage carrier drum 202 that is the direction of the arrow B. Even if thedamper 404 is fixed to the inner peripheral surface of the image carrierdrum 202 with an adhesive, the damper 404 can be moved in the directionof the arrow B by thrusting the damper 404 in the direction of the arrowB and breaking the adhesive.

Thus, by thrusting the force imparting member 413 in the direction ofthe arrow B, the sidewall 410 of the damper 404 that moves due topressure applied by the force imparting member 413 comes in contact withthe second flange 303A and pushes this flange as shown in FIG. 36.Therefore, the flange 303A is separated apart from the image carrierdrum 202. In this case also, when the flange 303A is fixed to the imagecarrier drum 202 with an adhesive, pushing the flange 303A results inbreaking the adhesive. When the force imparting member 413 is movedfurther in the direction of the arrow B, the damper 404 is alsoseparated apart from the image carrier drum 202. Then, the forceimparting member 413 is pulled out from the image carrier drum 202.Thus, the damper 404 and the flange 303A can be separated apart from theimage carrier drum 202 just by pushing the damper 404 by the forceimparting member 413 thereby enabling the disassembling of components ata low cost.

The damper 404 and the flanges 303 and 303A, having been disassembled inthe above manner, require only cleaning for reuse. Moreover, since thedamper 404 before being disassembled is disposed in the space surroundedby the image carrier drum 202, the flange 303 and the flange 303A, it isnot contaminated by either of dust and toner during the use of the imagecarrier drum 202. Therefore, the damper 404 can also be reused withoutcleaning after it is separated from the image carrier drum.

As explained above, in the method for inserting and removing the damperinto and from the image carrier drum of this example, the damper 404 isinserted into the image carrier drum 202 from the opening 411 on one endin the axial direction of the image carrier drum 202. The damper 404 ismounted inside the image carrier drum 202 and is removed from theopening 412 on the other end in the axial direction of the image carrierdrum 202. The drum unit 434 includes the image carrier drum 202 and thedamper 404. More specifically, the damper 404 is inserted into the imagecarrier drum 202 from the opening 411 on one end in the axial directionof the drum 202, mounted inside the image carrier drum 202, and thenremoved from the image carrier drum 202 through the opening 412 on theother end in the axial direction of the drum 202.

Based on the method as explained above, the damper 404 can be mountedinside the image carrier drum 202 or can be removed from the drum 202 bycarrying out simple operation thereby facilitating the recyclingprocess. Only the same operation is required for mounting and removingthe damper 404.

Besides, according to the method for inserting and removing the damperinto and from the image carrier drum of this example, the damper 404 ismoved in the axial direction of the image carrier drum 202 by exertingan external force on the damper 404 by the force imparting member 413and mounted inside the image carrier drum 202. Similarly, the damper 404is moved inside the image carrier drum 202 in its axial direction byexerting an external force by the force imparting member 413 and isremoved from the image carrier drum. The damper 404 is applied with anexternal force exerted by the force imparting member 413, is movedinside the image carrier drum 202 in its axial direction, and is mountedinside the image carrier drum 202. The damper 404 is applied with anexternal force exerted by the force imparting member 413, is movedinside the image carrier drum 202 in its axial direction, and is removedfrom the image carrier drum. Thus, operating the force imparting member413 enables the damper 404 to be inserted into and removed from theimage carrier drum 202 in a simple manner.

Moreover, when being inserted into and removed from the image carrierdrum 202, the damper 404 moves inside the image carrier drum 202 in theaxial direction of the drum. This direction is simply called a movementdirection. The sidewall 410 of the damper 404 is integrated in the frontend of the movement direction of the cylinder 417 of the damper 404. Theforce imparting member 413 is in contact and engaged with the sidewall410 and pushes the damper. Thus, the sidewall 410 of the damper 404forms an engaging portion with which the force imparting member 413 isengaged. Hereinafter, reference numeral 401 is assigned to this engagingportion formed with the sidewall 410.

As explained above, the damper 404 of this example includes the engagingportion 401 with which the force imparting member 413 is engaged on thefront end of the movement direction when the damper 404 moves inside theimage carrier drum 202 in the axial direction of the drum 202. The forceimparting member 413 exerts an external force on the engaging portion401 in the direction of movement of the damper 404 and moves the damper404 in the axial direction of the image carrier drum 202.

Thus, at least a part of the outer diameter of the damper 404 can bemade to contract by the external force applied by the force impartingmember 413 to the engaging portion 401 in the axial direction of theimage carrier drum 202. Therefore, the damper 404 can be moved smoothlyinside the image carrier drum 202. In other words, the damper 404 shownin the figure is made of an elastic material and the outer diameter ofthe damper 404 before insertion is set to be slightly bigger that theinner diameter of the image carrier drum 202. Therefore, when the damper404 is pushed slightly in the direction of the arrow B by the forceimparting member 413 as shown in FIG. 35, the damper 404 tends to stopfor a while due to the frictional force acting between the innerperipheral surface of the image carrier drum 202 and the outerperipheral surface 414 of the damper 404. However, by further pushingthe engaging portion 401 by the force imparting member 413, the damper404 made of an elastic material tends to be extended in the axialdirection, and the damper 404 undergoes elastic deformation in thedirection of contraction of the diameter as shown by an arrow C in FIG.35. Therefore, the damper 404 can be moved smoothly. Similar deformationoccurs when the damper 404 is pushed out from the image carrier drum.

When the force imparting member 413 pushes the rear end of the damper404 in its axial direction and the damper 404 is made of an elasticmaterial, the frictional force acting between the damper 404 and theinner peripheral surface of the image carrier drum 202 is exerted on thedamper 404. Therefore, the damper 404 expands in the radial therebyhindering the smooth movement of the damper 404. However, disposing theengaging portion 401 on the front end in the direction of movement ofthe damper 404 prevents such an inconvenience.

In the example explained above, the damper 404 is pushed by the forceimparting member 413 in the axial direction of the image carrier drum202 and is mounted inside the image carrier drum 202. Similarly, thedamper 404 is pushed by the force imparting member 413 in the axialdirection and is removed from the image carrier drum 202. The engagingportion 401 of the damper 404 is pushed by the force imparting member413 from one end to the other end of the image carrier drum 202 to movethe damper 404 inside the drum 202.

On the other hand, an engaging portion of a damper can be pulled by aforce imparting member from one end to the other end of the imagecarrier drum 202 to move the damper inside the drum 202. FIG. 38 is across section of an example of how a damper 404 is pulled out from animage carrier drum 202. A sidewall 410 of this damper 404 i.e. anengaging portion 401 has an engagement hole 435. A hook 450A is providedat a front end of a force imparting member 450 which is inserted insidethe image carrier drum 202 through a hole 436 at the center of theflange 303A. The hook 450K is engaged in the engagement hole 435. Bypulling the force imparting member 450 in the direction of an arrow B,the damper 404 can be removed from inside of the image carrier drum 202.In this case as well, the damper 404 pushes the flange 303A, andtherefore the flange 303A can be removed from the image carrier drum202. When the damper 404 is inserted into the image carrier drum 202,with a flange 303 separated apart from the image carrier drum 202, thehook 450A of the force imparting member 450 is engaged in the engagementhole 435 of the damper 404 and the damper 404 is pulled in the directionof the arrow B.

The rest of the structure other than the drum unit 434 shown in FIG. 38can also be structured similar to the drum unit explained earlier. Inthe case of the drum unit shown in FIG. 38, an external force is exertedby the force imparting member 450 on the engaging portion 401 in theaxial direction of the image carrier drum 202 to contract at least apart of the outer diameter of the damper 404. Therefore, the damper 404can be made to move smoothly inside the image carrier drum 202.

In the example explained above, as a force imparting member that movesthe damper 404 inside the image carrier drum 202, an exclusively madeforce imparting member 450 (450A) is used. However, as this forceimparting member, a shaft disposed inside the image carrier drum andsupporting the drum can also be used. FIG. 39 is a cross section of anexample of such type of force imparting member. In a drum unit 434 inthe figure, a shaft 437 passes through an image carrier drum 202 and ispress fitted into flanges 330 and 330A. A damper 404 shown in FIG. 39 issimilar to the damper 404 explained in the earlier example. The damper404 in FIG. 39 includes a cylinder 417 that has an outer peripheralsurface fixed to an inner peripheral surface of the image carrier drum202 and a sidewall 410 that is integrated on the front end in themovement direction of the cylinder 417. The sidewall 410 has an engagingportion 401. Moreover, the engaging portion 401 is formed by thesidewall 410 of the damper 404 that is disposed inside the image carrierdrum 202. The engaging portion 401 has a hole 438 having a diameterbigger than that of the shaft 437 that supports the image carrier drum202. The shaft 437 passes through the hole 438.

The shaft 437 is rotatably supported by the case 219 of the processcartridge 218 shown in FIG. 32. The shaft 437 is a component of theprocess cartridge 437. Moreover, the shaft 437 has a bigger diameterportion 439, which can be engaged with the engaging portion 401 of thedamper 404.

Following is a procedure for assembling the damper 404 inside the imagecarrier drum 202. The damper 404 is disposed on the left side of theimage carrier drum 202 in FIG. 39. The shaft 437 that is without theflanges 303 and 303A fixed is inserted into the drum 202 from theopening on the left end of the drum 202. The shaft 437 is further passedthrough the hole 438 in the damper 404. The engaging portion 401 of thedamper 404 is pushed by the bigger diameter portion 439 of the shaft437, and the damper 404 is pushed in the direction of the arrow B inFIG. 39. While the damper 404 is pushed, the shaft 437 together with thedamper 404 is inserted inside the image carrier drum 202. Then, theflanges 303 and 303A are fitted on the ends of the shaft 437 and also onthe openings at the ends of the image carrier drum 202. Thus, the damper404 is mounted inside the image carrier drum 202.

When the damper 404 is to be removed from the image carrier drum 202,the first flange 303 is pulled out from the shaft 437 first, and theshaft 437 is made to move in the direction shown by the arrow B in FIG.39, i.e. in the axial direction of the image carrier drum 202. Thebigger diameter portion 439 of the shaft 437 comes in contact with theengaging portion 401 of the damper 404 and pushes the portion 401 in thedirection of the arrow B. Due to this, the damper 404 moves in the axialdirection of the image carrier drum i.e. in the direction of the arrow Btogether with the shaft 437. When the damper 404 is fixed to the innerperipheral surface of the image carrier drum with an adhesive, thedamper 404 is pushed in the direction of the arrow B thereby breakingthe adhesive to allow the damper 404 to be moved further in thedirection of the arrow B. While doing this, the shaft 437 slides withrespect to the second flange 303A. When the shaft 437 is continued to bemoved in the direction of the arrow B, the damper 404 moving togetherwith the shaft 437 pushes the second flange 303A thereby separating theflange 303A apart from the image carrier drum 202 as shown in FIG. 40.When the shaft 437 is moved further in the direction of the arrow B, thedamper 404 is also separated apart from the image carrier drum 202. Whenthe flange 303A is fitted to the image carrier drum 202 by clearancefit, the flange 303A can also be separated from the image carrier drum202 before the damper 404 comes in contact with the flange 303A.

The structure can also be made such that the shaft 437 is supported bythe main body of the image forming apparatus, the shaft 437 is left onthe main body of the image forming apparatus, and the drum unit 434 ispulled out from the shaft 437 and can be fitted to the shaft 437 again.In such a case, the drum unit 434 is removed from the main body of theimage forming apparatus. Then, as shown in FIG. 34 to FIG. 37, thedamper 404 is removed from inside of the image carrier drum 202 using anexclusive force imparting member 413, or the damper 404 is mountedinside the drum 202 using the exclusive force imparting member 413.Thus, the damper 404 can be easily inserted into and removed from theimage carrier drum 202.

The rest of the structure of the drum unit 434 apart from those shown inFIG. 39 and FIG. 40 is similar to the structure shown in FIG. 32 to FIG.37.

The damper 404 can also be formed by a compression coil spring 440 asshown in FIG. 41. Due to its elastic nature, the compression coil spring440 is in pressed contact with the inner peripheral surface of the imagecarrier drum 202. Alternatively, the compression coil spring 440 canalso be fixed to the inner peripheral surface of the image carrier drum202 with an adhesive.

The damper 404 formed by the compression coil spring 440 is to beinserted into the image carrier drum 202 by following method. The firstflange 303 is separated from the image carrier drum 202, and a hook 450Aof a force imparting member 450 is engaged with an engaging portion 401Aat one end of the compression coil spring 440. The force impartingmember 450 is pulled in the direction of an arrow B thereby insertingthe damper 404 into the image carrier drum 202 from an opening 411 onone end in the axial direction of the drum 202.

When the damper 404 formed by the compression coil spring 440 is to beremoved, the compression coil spring 440 is pulled by the forceimparting member 450 in the direction of the arrow B in the same manneras explained above. Thus, the damper 404 formed by the compression coilspring 440 can be removed from the image carrier drum 202 through anopening 412 on the other end in the axial direction of the image carrierdrum 202. In this case, the compression coil spring 440 pushes thesecond flange 303A thereby removing the flange 303A from the imagecarrier drum 202. The rest of the structure can be formed similarly tothe example mentioned above. An external force is exerted on theengaging portion 401A in the axial direction of the image carrier drum202 by the force imparting member 450 to reduce at least a part of anouter diameter of the compression coil spring 440, and the compressioncoil spring 440 can be easily moved inside the image carrier drum 202.This action is similar to that in other structures.

Thus, as mentioned in the examples above, at least a portion of thedamper that is in contact with the inner wall surface of the imagecarrier drum 202 is formed by an elastic material. The damper 404 makesa pressed contact with the inner wall surface of the image carrier drum202 by the elastic nature i.e. restoring force, and is held inside thedrum 202. When the damper 404 is fixed to the image carrier drum 202without using an adhesive, it can be moved easily in the axial directioninside the image carrier drum 202.

In the example shown in FIG. 41, when the damper 404 that is to beremoved from the image carrier drum 202 is moved inside the drum 202,the damper 404 pushes the flange 303A fitted on the opening 412 on oneend in the axial direction of the image carrier drum 202 and separatesthe flange 303A apart from the image carrier drum 202. Thus, the flange303 can be separated apart from the image carrier drum 202 just bypushing action by the damper 404, which makes it possible to enhance theworkability.

When the flange 303A is fitted to the image carrier drum 202 by eitherof press fit and clearance fit without using an adhesive, the flange303A can be removed from the drum 202 when the damper 404 is removedfrom the drum 202. The flange 303A can be removed by using a smallamount of force and without any damage caused to it.

Moreover, as shown in FIG. 42, the second flange 303A can be structuredsuch that it has a cylindrical first flange member 415 that fits in theopening 412 at the end in the axial direction of the image carrier drum202 and a second flange member 416 that fits in the first flange member415. In this example, a gear 305 is formed on the first flange member415. This is similar to the case in the exploded perspective view inFIG. 30. Dimensions of flanges are basically the same as the dimensionsin FIG. 31.

This structure enables to disengage the second flange member 416 fromthe first flange member 415 using a small amount of force by pushing thesecond flange member 416 by the damper 404. Thus, the flange members 415and 416 can be separated apart easily from the image carrier drum 202without exerting considerable force. This prevents damage to the firstflange member 415 and the second flange member 416 and these flanges canbe reused in the existing condition. This structure can be also usedwhen the force imparting member is formed by the shaft 437 or when theforce imparting member is structured as shown in FIG. 38 and FIG. 41.

As shown in FIG. 42, it is also possible to form at least a part 410A ofa sidewall 410 of the damper 404 that pushes the second flange member416, with a rigid material like metal. Due to such a structure, theforce exerted by the force imparting member 413 can be transmitteddirectly to the second flange member 416, and the second flange member416 can be removed easily from the first flange member 415.

The other structures in the examples shown in FIG. 42 to FIG. 44 aresimilar to the examples explained above.

In the image forming apparatus shown in FIG. 32, the drum unit 434 andthe image forming units such as the charging roller 220, the developingunit 222, the cleaning unit 227 which form an image on the image carrierdrum 202 are integrally assembled to the process cartridge 218.Therefore, when the process cartridge 218 reaches end of its life, thecartridge may be replaced thereby facilitating maintenance of the imageforming apparatus.

It is a normal practice to reduce the size and weight of the processcartridge to make it easy to handle. Due to use of small sizedcomponents in the process cartridge, the life of the process cartridgeis short. In the image forming apparatus in FIG. 32, an arrangement ismade to replenish the toner container 233 with toner. However, if thereis no such an arrangement for replenishment of the toner and thestructure is made such that the process cartridge is replaced after thedeveloping unit is run out of the toner, the life of the processcartridge becomes further shorter. The short life of the processcartridge implies an increased number of process cartridges that aremade and are in the market. Therefore, it is important to facilitate thedisassembling of the image carrier drum 202, the damper 404, and theflanges 303 and 303A to improve recycling. This can be done in areliable manner by assembling or disassembling the image carrier drum202, the damper 404, and the flanges 303 and 303A as mentioned in theembodiment to enable easy recycling.

The image forming apparatus shown in FIG. 32 is structured such that atransferred toner image can be fixed on the recording medium P atcomparatively low temperature and a toner having a low melting point isused to enable conservation of energy. Concretely, the toner having alow melting point is used in the developing unit to enable the fixing ofthe toner image in the fixing unit at comparatively low surfacetemperature of the fixing roller, for example 145° C. The image formingapparatus forms a toner image on the image carrier drum using a tonerhaving an outflow start temperature less than or equal to 120° C.,preferably in a range of 99° C. to 102° C., measured by flow testermethod. The measurement of outflow start temperature by the flow testermethod is already explained above and hence omitted here.

A case of using the toner having a low melting point tends to generatenoise easily as compared to a case of using a toner having a highmelting point. It is not quite sure why the use of the toner having alow melting point increases the noise. However, It is considered thatadditive like wax contained in the toner tends to stick to the surfaceof the image carrier drum. Since the amount of the additive depositedbecomes non-uniform according to an image pattern, a component like thecleaning blade, which is in contact with the surface of the imagecarrier drum, does not move uniformly. Therefore, it is thought thatloud noise is produced in the image carrier drum due to vibrationscaused by non-uniform movement of the cleaning blade.

Therefore, it is desirable to use the damper 404 as explained earlier,which is made of a material having a tangent of loss tan δ greater thanor equal to 0.5. The tangent of loss tan δ is a tangent of a phase angleδ (loss angle) of stress and strain in a material. The greater the valueof the tangent of loss tan δ, the greater the damping effect is.Considering the characteristics of this type of damping material, thedamper 404 made of the material having a tangent of loss tan δ greaterthan or equal to 0.5 is provided inside the image carrier drum 202 toeffectively damp the rotating drum 202. By using the toner having a lowmelting point, it is possible to reduce the noise generated in therotating image carrier drum 202 during image formation to an extremelylow level. A rubber material such as butyl rubber and nitrile rubber canbe used as a material that has the tangent of loss tan δ greater than orequal to 0.5.

When a toner including a metallic salt of high fatty acid like zincstearate is used for the image forming apparatus, a part of the tonergets deposited on the surface of the image carrier drum 202. Due to thetoner deposited on the surface, the coefficient of friction of thecleaning blade 230 decreases thereby smoothening sliding of an edge ofthe cleaning blade 230. This reduces vibrations in the cleaning blade230 and improves the prevention of noise considerably.

The present invention can be applied to an image forming apparatus ofany form apart from that mentioned in FIG. 32. It can also be applied toan image forming apparatus shown in FIG. 43. In the image formingapparatus shown in FIG. 43, a charging roller 520 charges an imagecarrier drum 202 rotating in the direction of an arrow. The chargedsurface of the drum 202 is irradiated with a laser beam L emitted froman exposing unit (not shown) to form a first electrostatic latent imageon the image carrier drum 202. The electrostatic latent image isvisualized as a yellow toner image by a yellow developing device 522Y inthe developing unit 522. The yellow toner image is then transferred toan intermediate transfer belt 550 that is rotating in the direction ofan arrow E. A cleaning unit 527 cleans the surface of the image carrierdrum after transferring of the yellow image.

Similarly, a second electrostatic latent image is formed on the imagecarrier drum 202. The latent image is visualized as a magenta tonerimage by a magenta developing device 522M in the developing unit 522.This toner image is then transferred to the intermediate transfer belt550 and is superimposed on the yellow toner image, which has alreadybeen transferred. In a similar way, a cyan toner image and a black tonerimage are sequentially formed on the image carrier drum 202 by a cyandeveloping device 522C and a black developing device 522BK in thedeveloping unit 522 respectively, and these toner images aresuperposedly transferred to the intermediate transfer belt 550.

The superimposed toner images transferred to the intermediate transferbelt 550 are then transferred to a recording medium P that is fed from apaper feeding unit 551. When the recording medium passes through afixing unit 552, the toner images are fixed on the recording medium.

A damper 404 is mounted in the image carrier drum 202 of this imageforming apparatus. The damper 404 is inserted into the image carrierdrum 202 and then removed in the same manner as explained above. In acase of the image forming unit in FIG. 43, a process cartridge 518 canbe formed by assembling the image carrier drum 202, at least one imageforming unit for forming a toner image on the image forming drum, andthe intermediate transfer belt 550.

Thus, the embodiments in which the image carrier drum is formed by aphotoreceptor drum are explained above. These structures can also beused when the image carrier drum is formed by an intermediate transferdrum on which a toner image is transferred from the photoreceptor.

As explained above, according to the present invention, the vibrationabsorber is disposed on the side opposite to the surface facing the unitin which the bias characteristics for the latent image carrier are set.Therefore, due to the bias characteristics, the vibration absorber thatis in contact with the latent image carrier absorbs a part of thevibrations in the latent image carrier, which is caused by the vibratingelectric field generated when ac voltage is applied. This enables toreduce the resonance in the latent image carrier, thereby preventingnoise. Even if the latent image carrier is either of a belt and athin-walled cylinder in particular, noise can be prevented withoutincreasing the mass and without complicating the structure of the latentimage carrier.

Further, the vibration absorber is in the form of a roller and thestrong vibration absorbing material is provided either on the surface ofor inside the roller, and therefore even if the roller comes in contactwith the latent image carrier, the propagation of vibrations to thelatent image carrier is prevented. Thus, the noise due to resonance inthe latent image carrier is prevented.

Moreover, since the drive roller is used as the vibration absorber whenthe latent image carrier is in the form of a belt, a damper can be usedfor a material in firm contact with the latent image carrier. Thisfacilitates the absorption of vibrations generated in the latent imagecarrier and enables to reduce the resonance in the latent image carrierby using the existing structure.

When the latent image carrier is a belt, the vibration absorber isprovided on the opposite side to the surface of the supporting platewhich is in contact with the latent image carrier. The supporting plateis made of a rigid body in the form of a flat plate and is in contactwith the belt. Therefore, the vibration absorber absorbs the vibrationsgenerated in the belt without obstructing the movement, and resonance inthe latent image carrier can be reduced.

Since the vibration absorber is disposed in a position opposite to theunit in which the bias characteristics for the latent image carrier areset, the resonance can be reduced in the most efficient manner at theorigin of resonance in the latent image carrier due to the biascharacteristics.

When the latent image carrier is a substrate in the form of a thin beltand has a photosensitive layer on the surface of the substrate, thesubstrate is made of a material that absorbs strong vibrations.Therefore, the substrate can reduce it's own vibrations and there is noneed to have a special arrangement for damping and hence no extra cost.

By setting the value of the tangent of loss tan δ which affects thedamping effect to be greater than or equal to 0.5, the frequency ofresonance can be changed to the frequency band in which high frequencysound harsh to ears is not produced. Therefore, even when the noise isgenerated from the latent image carrier, the same effect as that ofreducing the noise can be achieved.

Since the vibration absorber is in the solid cylindrical form, it ispossible to change the resonance frequency of the latent image carrierto the low frequency band efficiently by using the difference in mass,unlike the hollow cylindrical form. Thus, the resonance caused by thevibrations of the latent image carrier can be prevented and noise can bereduced in efficient manner.

It is possible to reduce the material cost by using the vibrationabsorber in the hollow cylindrical form. In a case of the structure thatleads to the reduction in the material cost, in other words, even in acase where it is difficult to decrease the resonance frequency due tothe mass unlike a case of the solid cylindrical form, deterioration ofthe damping effect can be prevented reliably by setting the value of thetangent of loss tan δ, which affects the damping effect, to be greaterthan or equal to 0.6.

Moreover, since the vibration absorber is fitted inside the latent imagecarrier by either of press fitting and fixing by an adhesive, it isthoroughly integrated with the latent image carrier thereby reducing theresonance in the latent image carrier in efficient manner.

The generation of noise can be reduced effectively by using a tonerhaving a low melting point.

The cylinder unit can be disassembled easily thereby facilitatingrecycling.

The image carrier drum and the damper can be disassembled easily therebyfacilitating recycling.

The present document incorporates by reference the entire contents ofJapanese priority documents, 2002-169218 filed in Japan on Jun. 10,2002, 2002-170655 filed in Japan on Jun. 11, 2002, 2002-181552 filed inJapan on Jun. 21, 2002, 2002-195224 filed in Japan on Jul. 3, 2002 and2003-113709 filed in Japan on Apr. 18, 2003.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

1-42. (canceled)
 43. A method of insertion and removal of a damper intoand from an image carrier drum, comprising: inserting the damper intothe image carrier drum from an opening on one end in an axial directionof the image carrier drum and thereby mounting the damper inside thedrum; and removing the damper from an opening on other end in the axialdirection of the image carrier drum.
 44. The method according to claim43, wherein the inserting includes moving the damper in the axialdirection of the image carrier drum by exerting an external force by aforce imparting member to thereby mount the damper inside the drum, andthe removing includes moving the damper inside the drum in the axialdirection of the drum by exerting an external force by the forceimparting member to thereby remove the damper from the image carrierdrum.
 45. The method according to claim 44, wherein the force impartingmember is a shaft that is disposed inside the image carrier drum andsupports the image carrier drum.
 46. A drum unit comprising: an imagecarrier drum; and a damper, wherein the damper is inserted into theimage carrier drum from an opening on one end in an axial direction ofthe image carrier drum to thereby mount the damper inside the drum, andthe damper mounted inside the drum is removed from an opening on otherend in the axial direction of the image carrier drum.
 47. The drum unitaccording to claim 46, wherein the damper has elasticity and the damperis held inside the image carrier drum by a pressed contact due to theelasticity with an inner surface of the image carrier drum.
 48. The drumunit according to claim 46, wherein the damper is fixed with an adhesiveon an inner surface of the image carrier drum.
 49. The drum unitaccording to claim 46, further comprising a force imparting member,wherein the damper is moved in the axial direction of the image carrierdrum by exerting an external force by the force imparting member tothereby mount the damper inside the drum, and the damper is moved insidethe drum in the axial direction of the drum by exerting an externalforce by the force imparting member to thereby remove the damper fromthe image carrier drum.
 50. The drum unit according to claim 49, whereinthe damper has an engaging portion at the front end in the direction ofmovement when the damper moves in the axial direction inside the imagecarrier drum, in which the force imparting member engages and the damperis moved in the axial direction of the image carrier drum by theexternal force exerted by the force imparting member on the engagingportion in the direction of movement of the damper.
 51. The drum unitaccording to claim 50, wherein at least a part of an outer diameter ofthe damper is made to contract by the external force exerted by theforce imparting member on the engaging portion in the axial direction ofthe image carrier drum.
 52. The drum unit according to claim 50, whereinthe damper is moved inside the image carrier drum by pushing theengaging portion of the damper by the force imparting member from oneend to the other end of the image carrier drum.
 53. The drum unitaccording to claim 50, wherein the damper is moved inside the imagecarrier drum by pulling the engaging portion of the damper by the forceimparting member from one end towards the other end of the image carrierdrum.
 54. The drum unit according to claim 49, wherein the forceimparting member is a shaft that is disposed inside the image carrierdrum and supports the image carrier drum.
 55. The drum unit according toclaim 50, wherein the damper has a cylindrical portion, which has anouter peripheral surface that is fixed with respect to the innerperipheral surface of the image carrier drum; and an edge wall that isintegrated at the front end in the direction of movement of thecylindrical portion and the edge wall is included in the engagingportion.
 56. The drum unit according to claim 55, wherein the engagingportion, which includes the edge wall, has a hole of diameter biggerthan that of a shaft that supports the image carrier drum, and the shaftcan be passed through the hole.
 57. The drum unit according to claim 46,wherein the damper includes a compression coil spring.
 58. The drum unitaccording to claim 46, wherein, the damper that has to be removed fromthe image carrier drum when moved inside the image carrier drum, pushesand separates apart a flange that is fixed on the image carrier drum.59. The drum unit according to claim 58, wherein the flange is fitted tothe drum by either of press fit and clearance fit.
 60. The drum unitaccording to claim 58, wherein the flange includes a first flange memberthat fits in the opening on the other side in the axial direction of theimage carrier drum; and a second flange member that is fitted on thefirst flange member and makes the first flange member to have pressedcontact with the inner peripheral surface of the image carrier drum,wherein a front edge surface of the damper comes in contact with thesecond flange member and pushes the second flange member when the damperthat has to be removed from the image carrier drum is moved inside theimage carrier drum.
 61. An image forming module, comprising: a drum unithaving an image carrier drum; and a damper, wherein the damper isinserted into the image carrier drum from an opening on one end in anaxial direction of the image carrier drum to thereby mount the damperinside the drum, and the damper mounted inside the drum is removed froman opening on other end in the axial direction of the image carrierdrum; and an image forming unit that forms a toner image on the imagecarrier drum, wherein the drum unit and the image forming unit aredetachable from a main body of the image forming apparatus.
 62. An imageforming apparatus comprising an image forming module including a drumunit having an image carrier drum; and a damper, wherein the damper isinserted into the image carrier drum from an opening on one end in anaxial direction of the image carrier drum to thereby mount the damperinside the drum, and the damper mounted inside the drum is removed froman opening on other end in the axial direction of the image carrierdrum; and an image forming unit that forms a toner image on the imagecarrier drum, wherein the drum unit and the image forming unit aredetachable from a main body of the image forming apparatus.
 63. Theimage forming apparatus according to claim 62, wherein the toner imageis formed on the image carrier drum using a toner having outflow starttemperature lower than or equal to 102° C. measured by flow testermethod and the damper is made of a material that has a tangent of losstan δ greater than or equal to 0.5.
 64. An image forming apparatuscomprising a drum unit having an image carrier drum to form a tonerimage; and a damper, wherein the damper is inserted into the imagecarrier drum from an opening on one end in an axial direction of theimage carrier drum to thereby mount the damper inside the drum, and thedamper mounted inside the drum is removed from an opening on other endin the axial direction of the image carrier drum.
 65. The image formingapparatus according to claim 64, wherein the toner image is formed onthe image carrier drum using a toner having outflow start temperaturelower than or equal to 102° C. measured by flow tester method and thedamper is made of a material that has a tangent of loss tan δ greaterthan or equal to 0.5.